The information in this preliminary prospectus supplement is not complete and may be changed. A registration statement relating to these securities has become effective immediately upon filing by rule of the Securities and Exchange Commission. This preliminary prospectus supplement and the accompanying prospectus are not an offer to sell these securities, and we are not soliciting offers to buy these securities in any state where the offer or sale is not permitted.

Filed Pursuant to Rule 424(b)(5)
Registration No. 333-200216

Subject to Completion
Preliminary Prospectus Supplement dated April 6, 2015

PROSPECTUS SUPPLEMENT
(To Prospectus Dated November 14, 2014)

7,000,000 Shares

Dyax Corp.

[GRAPHIC MISSING]

Common Stock

We are offering 7,000,000 shares of our common stock.

Our common stock is traded on The Nasdaq Global Market under the symbol “DYAX.” On April 2, 2015 the last reported sale price of our common stock was $27.05 per share.

Investing in our common stock involves risks. See “Risk Factors” on page S-4 of this prospectus supplement.


	Per Share	Total
Public offering price	$	$
Underwriting discounts and commissions⁽¹⁾	$	$
Proceeds, before expenses, to us	$	$

(1)

See “Underwriting” for additional disclosure regarding underwriting discounts, commissions and estimated offering expenses.

The underwriters may also purchase up to an additional 1,050,000 shares of common stock from us at the public offering price, less the underwriting discounts and commissions payable by us, within 30 days of the date of this prospectus supplement.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus supplement or the accompanying prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

The shares will be ready for delivery on or about , 2015.


BofA Merrill Lynch		Cowen and Company		RBC Capital Markets


Needham & Company		Wedbush PacGrow

Prospectus Supplement dated , 2015

TABLE OF CONTENTS


	Page
Prospectus Supplement
ABOUT THIS PROSPECTUS SUPPLEMENT		S-ii
PROSPECTUS SUPPLEMENT SUMMARY		S-1
RISK FACTORS		S-4
FORWARD-LOOKING STATEMENTS		S-5
USE OF PROCEEDS		S-6
DIVIDEND POLICY		S-6
CAPITALIZATION		S-7
DILUTION		S-9
UNDERWRITING		S-11
LEGAL MATTERS		S-17
EXPERTS		S-17
WHERE YOU CAN FIND MORE INFORMATION		S-17
INCORPORATION OF CERTAIN INFORMATION BY REFERENCE		S-18

Prospectus


ABOUT THIS PROSPECTUS			1
DYAX CORP.			1
RISK FACTORS			3
FORWARD-LOOKING STATEMENTS			3
USE OF PROCEEDS			4
RATIO OF EARNINGS TO FIXED CHARGES AND RATIO OF COMBINED FIXED CHARGES AND PREFERRED STOCK DIVIDENDS TO EARNINGS			4
DESCRIPTION OF CAPITAL STOCK			5
DESCRIPTION OF DEBT SECURITIES			9
DESCRIPTION OF WARRANTS			16
DESCRIPTION OF UNITS			18
PLAN OF DISTRIBUTION			20
LEGAL MATTERS			22
EXPERTS			22
WHERE YOU CAN FIND MORE INFORMATION			22
INCORPORATION OF CERTAIN INFORMATION BY REFERENCE			23

S-i

TABLE OF CONTENTS

ABOUT THIS PROSPECTUS SUPPLEMENT

This document is in two parts. The first part is the prospectus supplement, which describes the terms of this offering and also adds to and updates information contained in the accompanying prospectus and the documents incorporated by reference into this prospectus supplement and the accompanying prospectus. The second part is the accompanying prospectus, which provides more general information, some of which may not apply to this offering. Generally, when we refer to this prospectus, we are referring to both parts of this document combined. To the extent there is a conflict between the information contained in this prospectus supplement, on the one hand, and the information contained in the accompanying prospectus or the documents incorporated by reference, on the other hand, you should rely on the information in this prospectus supplement.

You should rely only on the information incorporated by reference or provided in this prospectus supplement, the accompanying prospectus and in any free writing prospectus to which we have referred you. We have not authorized anyone to provide you with different information. If anyone provides you with different or inconsistent information, you should not rely on it. This prospectus supplement and the accompanying prospectus do not constitute an offer to sell, or a solicitation of an offer to purchase, the securities offered by this prospectus supplement and the accompanying prospectus in any jurisdiction where it is unlawful to make such offer or solicitation. You should not assume that the information contained in this prospectus supplement, the accompanying prospectus, any document incorporated by reference in this prospectus supplement or the accompanying prospectus, or any free writing prospectus to which we refer you is accurate as of any date other than the date on the front cover of the applicable document. Neither the delivery of this prospectus supplement nor any distribution of securities pursuant to this prospectus supplement shall, under any circumstances, create any implication that there has been no change in the information set forth or incorporated by reference into this prospectus supplement or in our affairs since the date of this prospectus supplement. Our business, financial condition, results of operations and prospects may have changed since that date.

Before purchasing any securities, you should carefully read this prospectus supplement, the accompanying prospectus, and any free writing prospectus we refer you to, together with the additional information described under the headings, “Where You Can Find More Information” and “Incorporation of Certain Information by Reference” in this prospectus supplement.

Unless the context otherwise requires, references in this prospectus supplement to “we,” “us” and “our” refer to Dyax Corp. and its consolidated subsidiaries.

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PROSPECTUS SUPPLEMENT SUMMARY

This summary highlights information contained elsewhere or incorporated by reference in this prospectus supplement and the accompanying prospectus. This summary does not contain all of the information that you should consider before deciding to invest in our common stock. You should read this entire prospectus supplement and the accompanying prospectus carefully, including the “Risk Factors” section, our consolidated financial statements and the related notes and the other information incorporated by reference in this prospectus supplement and the accompanying prospectus. In addition, certain statements include forward-looking information that involves risks and uncertainties. See “Forward-Looking Statements.”

Dyax Corp.

We are a biopharmaceutical company focused on:

•

Hereditary Angioedema and Other Plasma-Kallikrein-Mediated (PKM) Disorders

We develop and commercialize treatments for hereditary angioedema (HAE) and are working to identify additional disorders that are mediated by plasma kallikrein.

We discovered and developed KALBITOR, a small protein plasma kallikrein inhibitor, and are selling it in the United States for the treatment of acute attacks of HAE. Additionally, we discovered and are developing DX-2930, a fully human monoclonal antibody inhibitor of plasma kallikrein, which we believe is a candidate to treat HAE prophylactically. On March 31, 2015, we announced positive safety, pharmacokinetic, biomarker, and efficacy results from our Phase 1b clinical study of DX-2930. In addition, we announced receipt of Fast Track designation from the U.S. Food and Drug Administration (FDA) for the investigation of DX-2930 for HAE. Our patent rights related to DX-2930 include U.S. Patent No. 8,816,055, which contains claims covering the specific sequence of DX-2930, and U.S. Patent No. 8,822,653, which contains claims covering monoclonal antibodies that bind to the active form of human plasma kallikrein and do not bind human pre-kallikrein. Both patents are expected to provide coverage for DX-2930 until at least 2032.

•

Licensing and Funded Research Portfolio

We have a portfolio of product candidates being developed by licensees using our phage display technology. This portfolio currently includes one approved product, CYRAMZA® (ramucirumab) which is marketed by Eli Lilly and Company (Lilly), and multiple product candidates in various stages of clinical development for which we are eligible to receive future royalties and/or milestone payments.

Recent Developments

Preliminary financial information

KALBITOR gross sales for the quarter ended March 31, 2015 were approximately $17.6 million; subject to final adjustments for gross to net sales data, net sales are estimated to be in a range of $15.6 to $16.0 million. In addition, cash, cash equivalents and short-term investments totaled approximately $181.9 million at March 31, 2015.

The preliminary financial results presented above are subject to the completion of our financial closing procedures. Those procedures have not been completed. Accordingly, these results may change and those changes may be material.

The preliminary financial data included in this prospectus supplement has been prepared by and is the responsibility of Dyax's management. PricewaterhouseCoopers LLP has not audited, reviewed, compiled or performed any procedures with respect to the accompanying preliminary financial data. Accordingly, PricewaterhouseCoopers LLP does not express an opinion or any other form of assurance with respect thereto.

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Our History

We incorporated in Delaware in 1989 and merged with Protein Engineering Corporation in August 1995. Our principal executive offices are located at 55 Network Drive, Burlington, Massachusetts 01803 and our telephone number is (617) 225-2500.

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THE OFFERING

Issuer

Dyax Corp.

Common stock offered

7,000,000 shares

Common stock to be outstanding after this offering

143,662,175 shares (or 144,712,175 shares if the underwriters exercise their option to purchase additional shares in full).

Option to purchase additional shares

The underwriters may purchase up to an additional 1,050,000 shares of common stock from us at the public offering price, less the underwriting discounts and commissions payable by us, within 30 days of the date of this prospectus supplement.

Use of proceeds

We intend to use the net proceeds from this offering (i) to develop and, if approved, commercialize DX-2930 worldwide for the prophylactic treatment of HAE; (ii) for research and development of product candidates to address additional PKM disorders and other orphan diseases outside the PKM pathway, (iii) to prepay all of the debt outstanding under our loan agreement with LFRP Investors, L.P., an affiliate of HealthCare Royalty Partners (“HC Royalty”), which we refer to herein as the HC Royalty Loan, and (iv) for general corporate purposes. We will retain broad discretion to allocate the net proceeds. See “Use of Proceeds” on page S-6.

Nasdaq Global Market Symbol

“DYAX”

Risk factors

See “Risk Factors” and other information included in this prospectus supplement, the accompanying prospectus and the documents incorporated by reference in this prospectus supplement and the accompanying prospectus for a discussion of factors you should carefully consider before deciding to invest in shares of our common stock.

The total shares of common stock outstanding immediately after this offering is based on 136,662,175 shares outstanding as of December 31, 2014 and excludes as of that date:

•

22,446,202 shares of our common stock reserved for issuance under our 1995 Equity Incentive Plan, as amended, of which 11,587,079 shares are issuable upon exercise of outstanding stock options (at a weighted average exercise price of $4.11 per share) and 10,372,949 shares remain available for future grant;

•

486,174 shares issuable under outstanding restricted stock units; and

•

702,752 shares of common stock reserved for issuance under our 1998 Employee Stock Purchase Plan, of which 652,752 shares remain available for future grant.

Unless otherwise indicated, all information contained in this prospectus supplement assumes:

•

No exercise of the underwriters’ option to purchase an additional 1,050,000 shares of our common stock; and

•

No exercise of outstanding options to purchase shares of common stock.

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RISK FACTORS

An investment in our common stock involves a high degree of risk. You should carefully consider the risk factors discussed below and under the heading “Risk Factors” contained in our most recently filed periodic reports filed with the SEC, including our Annual Report on Form 10-K for the fiscal year ended December 31, 2014, which are incorporated by reference into this prospectus supplement. Before making an investment decision, you should carefully consider these risks as well as other information we include or incorporate by reference in this prospectus supplement. Additional risks and uncertainties not presently known to us or that we deem currently immaterial may also impair our business, operating results and financial condition and could result in a complete loss of your investment.

Risks Related to this Offering and Our Common Stock

We have broad discretion in the use of the net proceeds from this offering and our existing cash and may not use them effectively.

Our management will have broad discretion in the application of the net proceeds from this offering, including for any of the purposes described in the section entitled “Use of Proceeds,” as well as our existing cash, and you will be relying on the judgment of our management regarding such application. You will not have the opportunity, as part of your investment decision, to assess whether the proceeds are being used appropriately. Our management might not apply the net proceeds or our existing cash in ways that ultimately increase the value of your investment. If we do not invest or apply the net proceeds from this offering or our existing cash in ways that enhance stockholder value, we may fail to achieve expected financial results, which could cause our stock price to decline. Pending their use, we may invest the net proceeds from this offering in short-term, investment-grade, interest-bearing securities. These investments may not yield a favorable return to our stockholders.

If you purchase our common stock in this offering, you will incur immediate and substantial dilution in the book value of your shares.

Investors purchasing shares of common stock in this offering will pay a price per share that substantially exceeds the pro forma book value per share of our tangible assets as of December 31, 2014 after subtracting our liabilities. As a result, investors purchasing shares of common stock in this offering will incur immediate dilution of $25.09 per share, based on the difference between the assumed public offering price of $27.05 per share, the closing price on the Nasdaq Global Market on April 2, 2015, and the as adjusted pro forma net tangible book value per share of our outstanding common stock as of December 31, 2014, after giving effect to the application of the net proceeds of this offering to repay the principal balance outstanding under the HC Royalty Loan, which was $84,472,329 as of December 31, 2014. In addition, as of December 31, 2014, options to purchase 11,587,079 shares of our common stock at a weighted average exercise price of $4.11 per share were outstanding. The exercise of any of these options would result in additional dilution. As a result of the dilution to investors purchasing shares in this offering, investors may receive significantly less than the purchase price paid in this offering, if anything, in the event of our liquidation. Further, because we will need to raise additional capital to fund our clinical development programs, we may in the future sell substantial amounts of common stock or securities convertible into or exchangeable for common stock. These future issuances of common stock or common stock-related securities, together with the exercise of outstanding options and any additional shares issued in connection with acquisitions, if any, may result in further dilution. For a further description of the dilution that you will experience immediately after this offering, see “Dilution.”

If we sell shares of our common stock in future financings, stockholders may experience immediate dilution and, as a result, our stock price may decline.

We may from time to time issue additional shares of our common stock or securities convertible into our common stock, including in future financings or similar arrangements. For example, we issued 9,200,000 shares of our common stock during an offering in March 2014. If we issue additional shares of our common stock, our stockholders may experience immediate dilution and, as a result, our stock price may decline.

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FORWARD-LOOKING STATEMENTS

This prospectus supplement, the accompanying prospectus and the documents incorporated by reference in these documents include forward-looking statements within the meaning of Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended, including statements regarding the results from our Phase 1b study, which may not be predictive of the results or success of future clinical trials that will be required to permit application for regulatory approval of DX-2930; prospects for therapeutic benefits and clinical development of DX-2930 and the expected timing of clinical trial results; our dependence on the expertise, effort, priorities and contractual obligations of third parties in the manufacture, quality control, storage and clinical development of DX-2930; the potential benefits and usage of KALBITOR® (ecallantide) for treating HAE; the commercial potential of KALBITOR, including revenues and costs; estimates of potential markets for our products and product candidates; prospects for future milestone payments and/or royalties with respect to licensee product candidates in our Licensing and Funded Research Portfolio (LFRP); the potential for market approval for KALBITOR in markets outside the United States; plans to enter into additional collaborative and licensing arrangements for ecallantide and for other compounds in development; the sufficiency of our cash, cash equivalents and short-term investments; and expected future revenues, operating results and cash flows.

We have based these forward-looking statements on our current expectations and projections about future events. Our actual results could differ materially from those discussed in, or implied by, these forward-looking statements. Any statement that is not a statement of historical fact should be considered a forward-looking statement. We often use words or phrases of expectation or uncertainty like “believe,” “anticipate,” “plan,” “expect,” “intent,” “project,” “future,” “may,” “will,” “could,” “would” and similar words to help identify forward-looking statements.

Forward-looking statements involve risks and uncertainties. Our actual results could differ significantly from the results discussed in these forward-looking statements, which include, but are not necessarily limited to, those relating to: regulatory review and potential approval of our product candidates; our financial resources and future use of cash; future product research and development activities, including preclinical studies, clinical trials and collaborations; and competition.

Many factors could cause or contribute to these differences, including the factors described above under the caption “Risk Factors.” We caution you not to place undue reliance on our forward-looking statements, which speak only as of the date on which they are made. We undertake no obligation to update or revise any forward-looking statements, whether as a result of new information, future events or otherwise. You should carefully read this entire prospectus supplement, the accompanying prospectus and the documents incorporated by reference in these documents, particularly the section entitled “Risk Factors,” before you make an investment decision.

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USE OF PROCEEDS

At the assumed public offering price of $27.05 per share, the last reported sale price of our common stock on The Nasdaq Global Market on April 2, 2015, we estimate that the net proceeds from the sale of 7,000,000 shares of our common stock in this offering will be approximately $177.8 million (or $204.5 million if the underwriters exercise their option to purchase additional shares in full) after deducting the estimated underwriting discounts and commissions and estimated offering expenses payable by us.

Each $1.00 increase (decrease) in the assumed public offering price of $27.05 would increase (decrease) the net proceeds to us from this offering by approximately $6.6 million, after deducting estimated underwriting discounts and commissions and estimated offering expenses payable by us, assuming that the number of shares offered by us, as set forth above, remains the same. Each increase (decrease) of 100,000 shares in the number of shares offered by us at the assumed public offering price would increase (decrease) the net proceeds to us in this offering by approximately $2.5 million. We do not expect that a change in the public offering price or the number of shares by these amounts would have a material effect on our uses of the proceeds from this offering, although it may impact the amount of time prior to which we will need to seek additional capital.

We intend to use the net proceeds from this offering (i) to develop and, if approved, commercialize DX-2930 worldwide for the prophylactic treatment of HAE; (ii) for research and development of product candidates to address additional PKM disorders and other orphan diseases outside the PKM pathway, (iii) to prepay all of the debt outstanding under our loan agreement with LFRP Investors, L.P., an affiliate of HC Royalty, which we refer to herein as the HC Royalty Loan and (iv) for general corporate purposes. The HC Royalty Loan is pursuant to a loan agreement with LFRP Investors, L.P., an affiliate of HC Royalty, and matures on August 22, 2018. The loan bears interest at a rate of 12% per annum payable quarterly and can be repaid, in whole or in part, without penalty after August 20, 2015. We intend to repay the loan once the prepayment penalty period expires.

We have not determined the amounts we plan to spend on any of the areas listed above or the timing of these expenditures. As a result, our management will have broad discretion to allocate the net proceeds to us from this offering and investors will be relying on the judgment of our management regarding the application of the proceeds from this offering. We reserve the right to change the use of these proceeds as a result of certain contingencies such as competitive developments, the results of our commercialization efforts, acquisition and investment opportunities and other factors. Pending application of the net proceeds for specified purposes, we intend to temporarily invest the proceeds in short-term interest bearing instruments.

DIVIDEND POLICY

We have never declared or paid cash dividends on our capital stock. We currently intend to retain our future earnings, if any, for use in our business and therefore do not anticipate paying cash dividends in the foreseeable future. Payment of future dividends, if any, will be at the discretion of our board of directors after taking into account various factors, including our financial condition, operating results, current and anticipated cash needs and plans for expansion. In addition, the HC Royalty Loan restricts our ability to pay dividends.

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CAPITALIZATION

The following table sets forth our consolidated cash, cash equivalents and short-term investments and our capitalization as of December 31, 2014:

•

on an actual basis; and

•

on an adjusted basis after giving effect to (i) our sale of 7,000,000 shares of common stock offered hereby at an assumed public offering price of $27.05 per share, the last reported sale price of our common stock on The Nasdaq Global Market on April 2, 2015, (ii) the application of the net proceeds of this offering to repay the principal balance outstanding under the HC Royalty Loan, which was $84,472,329, in each case as if it had occurred on December 31, 2014, and (iii) after deducting the estimated underwriting discounts and commissions and estimated offering expenses payable by us.

You should read this table along with our historical consolidated financial statements and related notes and the other financial information included and incorporated by reference in this prospectus supplement and the accompanying prospectus.


	As of December 31, 2014
	Actual			As Adjusted⁽¹⁾
	(In thousands)
Cash, cash equivalents, and short-term investments	$	184,652		$	277,969
Note payable⁽²⁾		82,165			—
Stockholders’ deficit:
Preferred stock, $0.01 par value; 1,000,000 shares authorized; 0 shares issued and outstanding actual and as adjusted		—
Common stock, $0.01 par value; 200,000,000 shares authorized; 136,662,175 shares issued and outstanding, actual; and 143,662,175 shares issued and outstanding, as adjusted		1,367			1,437
Additional paid-in capital		650,249			827,968
Accumulated deficit		(545,841	)		(548,148	)
Accumulated other comprehensive income		28			28
Total stockholders’ equity		105,803			281,285
Total capitalization	$	187,968		$	281,285

(1)

Each $1.00 increase (decrease) in the assumed public offering price of $27.05 per share, the last reported sale price of our common stock on The Nasdaq Global Market on April 2, 2015, would increase (decrease) each of cash, cash equivalents and short-term investments, total stockholders’ equity and total capitalization by approximately $6.6 million, assuming that the number of shares offered by us, as set forth on the cover page of this prospectus supplement, remains the same, and after deducting estimated underwriting discounts and commissions and estimated offering expenses payable by us. We may also increase or decrease the number of shares we are offering. Each increase (decrease) of 100,000 shares in the number of shares offered by us would increase (decrease) each of cash, cash equivalents and short-term investments, total stockholders’ equity and total capitalization by approximately $2.5 million, assuming that the assumed public offering price remains the same, and after deducting the estimated underwriting discounts and commissions and estimated offering expenses payable by us. The as adjusted information discussed above is illustrative only and will adjust based on the actual public offering price and other terms of this offering determined at pricing.

(2)

In light of the prepayment penalty applicable to the HC Royalty Loan, we do not anticipate repaying this note payable until after August 20, 2015.

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The number of shares of common stock reflected in the discussion and tables above is based on 136,662,175 shares outstanding as of December 31, 2014 and excludes as of that date:

•

486,174 shares issuable under outstanding restricted stock units; and

•

702,752 shares of common stock reserved for issuance under our 1998 Employee Stock Purchase Plan, of which 652,752 shares remain available for future grant.

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DILUTION

If you invest in our common stock, your interest in the common stock may be diluted to the extent of the difference between the price you pay for each share of common stock and the net tangible book value per share of our common stock immediately after this offering. Net tangible book value per share of our common stock is determined at any date by subtracting our total liabilities from the amount of our total tangible assets (total assets less intangible assets) and dividing the difference by the number of shares of our common stock deemed to be outstanding at that date.

As of December 31, 2014, our net tangible book value was $105.4 million, or approximately $0.77 per share. After giving effect to (i) our sale of 7,000,000 shares of common stock in this offering at an assumed public offering price of $27.05 per share, the last reported sale price of our common stock on The Nasdaq Global Market on April 2, 2015, after deducting estimated underwriting discounts and commissions and estimated offering expenses payable by us and (ii) the application of the net proceeds of this offering to repay the principal balance outstanding under the HC Royalty Loan, which was $84,472,329 as of December 31, 2014, our as adjusted net tangible book value as of December 31, 2014 would have been $280.9 million or $1.96 per share. This amount represents an immediate increase in net tangible book value of $1.19 per share of common stock to existing stockholders and an immediate dilution in net tangible book value of $25.09 per share to purchasers in this offering, as illustrated in the following table:


Assumed public offering price per share of common stock			$	27.05
Net tangible book value per share as of December 31, 2014	$	0.77
Increase in net tangible book value per share attributable to this offering		1.19
As adjusted net tangible book value per share as of December 31, 2014 after giving effect to the offering				1.96
Dilution per share to new investors			$	25.09

Each $1.00 increase (decrease) in the assumed public offering price of $27.05 per share would increase (decrease) the as adjusted net tangible book value per share after this offering by approximately $0.04 and dilution per share to new investors by approximately $0.96, assuming that the number of shares offered by us, as set forth on the cover page of this prospectus supplement, remains the same and after deducting estimated underwriting discounts and commissions and estimated offering expenses payable by us.

We may also increase or decrease the number of shares we are offering. Each increase of 100,000 shares in the number of shares offered by us would increase our as adjusted net tangible book value per share after this offering by approximately $0.01 per share and decrease the dilution to new investors by approximately $0.01 per share, assuming that the public offering price remains the same and after deducting estimated underwriting discounts and commissions and estimated offering expenses payable by us. Each decrease of 100,000 shares in the number of shares offered by us would decrease our as adjusted net tangible book value per share after this offering by approximately $0.01 per share and increase the dilution to new investors by approximately $0.01 per share, assuming that the public offering price remains the same and after deducting estimated underwriting discounts and commissions and estimated offering expenses payable by us.

The information above assumes that the underwriters do not exercise their option to purchase additional shares. If the underwriters exercise their option to purchase additional shares of our common stock in full, the as adjusted net tangible book value per share after giving effect to this offering would be $2.13 per share, which amount represents an immediate increase in as adjusted net tangible book value of $1.36 per share of our common stock to existing stockholders and an immediate dilution per share to new investors in this offering of $24.92 per share.

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The discussion and table above are based on 136,662,175 shares outstanding as of December 31, 2014 and exclude as of that date:

•

486,174 shares issuable under outstanding restricted stock units; and

•

702,752 shares of common stock reserved for issuance under our 1998 Employee Stock Purchase Plan, of which 652,752 shares remain available for future grant.

To the extent that any of these shares are issued upon exercise of stock options or vesting of restricted stock units, there may be further dilution to new public investors. In addition, we may choose to raise additional capital due to market conditions or strategic considerations even if we believe we have sufficient funds for our current or future operating plans. To the extent that we raise additional capital by issuing equity securities or convertible debt, your ownership will be further diluted.

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UNDERWRITING

Merrill Lynch, Pierce, Fenner & Smith Incorporated and Cowen and Company, LLC are acting as representatives of each of the underwriters named below. Subject to the terms and conditions set forth in an underwriting agreement among us and the underwriters, we have agreed to sell to the underwriters, and each of the underwriters has agreed, severally and not jointly, to purchase from us, the number of shares of common stock set forth opposite its name below.


Underwriter		Number of Shares
Merrill Lynch, Pierce, Fenner & Smith Incorporated
Cowen and Company, LLC
RBC Capital Markets, LLC
Needham & Company, LLC
Wedbush Securities Inc.
Total

Subject to the terms and conditions set forth in the underwriting agreement, the underwriters have agreed, severally and not jointly, to purchase all of the shares sold under the underwriting agreement if any of these shares are purchased. If an underwriter defaults, the underwriting agreement provides that the purchase commitments of the nondefaulting underwriters may be increased or the underwriting agreement may be terminated.

We have agreed to indemnify the underwriters against certain liabilities, including liabilities under the Securities Act, or to contribute to payments the underwriters may be required to make in respect of those liabilities.

The underwriters are offering the shares, subject to prior sale, when, as and if issued to and accepted by them, subject to approval of legal matters by their counsel, including the validity of the shares, and other conditions contained in the underwriting agreement, such as the receipt by the underwriters of officer’s certificates and legal opinions. The underwriters reserve the right to withdraw, cancel or modify offers to the public and to reject orders in whole or in part.

Commissions and Discounts

The representatives have advised us that the underwriters propose initially to offer the shares to the public at the public offering price set forth on the cover page of this prospectus and to dealers at that price less a concession not in excess of $ per share. After the initial offering, the public offering price, concession or any other term of the offering may be changed.

The following table shows the public offering price, underwriting discount and proceeds before expenses to us. The information assumes either no exercise or full exercise by the underwriters of their option to purchase additional shares.

Per Share

Without
Option

With
Option

Public offering price

Underwriting discount

Proceeds, before expenses, to Dyax

The expenses of the offering, not including the underwriting discount, are estimated at $200,000 and are payable by us.

Option to Purchase Additional Shares

We have granted an option to the underwriters, exercisable for 30 days after the date of this prospectus, to purchase up to 1,050,000 additional shares at the public offering price, less the underwriting discount. If the

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underwriters exercise this option, each will be obligated, subject to conditions contained in the underwriting agreement, to purchase a number of additional shares proportionate to that underwriter’s initial amount reflected in the above table.

No Sales of Similar Securities

We and our executive officers and directors have agreed, for a period of 60 days after the date of this prospectus supplement, not to sell or transfer any common stock or securities convertible into, exchangeable for, exercisable for, or repayable with common stock, without first obtaining the written consent of Merrill Lynch, Pierce, Fenner & Smith Incorporated and Cowen and Company, LLC. Specifically, we and these other persons have agreed, with certain limited exceptions, not to directly or indirectly

•

offer, pledge, sell or contract to sell any common stock,

•

sell any option or contract to purchase any common stock,

•

purchase any option or contract to sell any common stock,

•

grant any option, right or warrant for the sale of any common stock,

•

lend or otherwise dispose of or transfer any common stock,

•

request or demand that we file a registration statement related to the common stock, or

•

enter into any swap or other agreement that transfers, in whole or in part, the economic consequence of ownership of any common stock whether any such swap or transaction is to be settled by delivery of shares or other securities, in cash or otherwise.

This lock-up provision applies to common stock and to securities convertible into or exchangeable or exercisable for or repayable with common stock. It also applies to common stock owned now or acquired later by the person executing the agreement or for which the person executing the agreement later acquires the power of disposition. In the event that either (x) during the last 17 days of the lock-up period referred to above, we issue an earnings release or material news or a material event relating to the Company occurs or (y) prior to the expiration of the lock-up period, we announce that we will release earnings results or become aware that material news or a material event will occur during the 16-day period beginning on the last day of the lock-up period, the restrictions described above shall continue to apply until the expiration of the 18-day period beginning on the issuance of the earnings release or the occurrence of the material news or material event.

Nasdaq Global Market Listing

Our common stock is listed on the Nasdaq Global Market under the symbol “DYAX.”

Price Stabilization, Short Positions

Until the distribution of the shares is completed, SEC rules may limit underwriters and selling group members from bidding for and purchasing our common stock. However, the representatives may engage in transactions that stabilize the price of the common stock, such as bids or purchases to peg, fix or maintain that price.

In connection with the offering, the underwriters may purchase and sell our common stock in the open market. These transactions may include short sales, purchases on the open market to cover positions created by short sales and stabilizing transactions. Short sales involve the sale by the underwriters of a greater number of shares than they are required to purchase in the offering. “Covered” short sales are sales made in an amount not greater than the underwriters’ option to purchase additional shares described above. The underwriters may close out any covered short position by either exercising their option to purchase additional shares or purchasing shares in the open market. In determining the source of shares to close out the covered short position, the underwriters will consider, among other things, the price of shares available for purchase in the open market as compared to the price at which they may purchase shares through the option granted to them. “Naked” short sales are sales in excess of such option. The underwriters must close out any naked short position by purchasing shares in the open market. A naked short position is more likely to be created if

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the underwriters are concerned that there may be downward pressure on the price of our common stock in the open market after pricing that could adversely affect investors who purchase in the offering. Stabilizing transactions consist of various bids for or purchases of shares of common stock made by the underwriters in the open market prior to the completion of the offering.

Similar to other purchase transactions, the underwriters’ purchases to cover the syndicate short sales may have the effect of raising or maintaining the market price of our common stock or preventing or retarding a decline in the market price of our common stock. As a result, the price of our common stock may be higher than the price that might otherwise exist in the open market. The underwriters may conduct these transactions on the Nasdaq Global Market, in the over-the-counter market or otherwise.

Neither we nor any of the underwriters make any representation or prediction as to the direction or magnitude of any effect that the transactions described above may have on the price of our common stock. In addition, neither we nor any of the underwriters make any representation that the representatives will engage in these transactions or that these transactions, once commenced, will not be discontinued without notice.

Passive Market Making

In connection with this offering, underwriters and selling group members may engage in passive market making transactions in the common stock on the Nasdaq Global Market in accordance with Rule 103 of Regulation M under the Exchange Act during a period before the commencement of offers or sales of common stock and extending through the completion of distribution. A passive market maker must display its bid at a price not in excess of the highest independent bid of that security. However, if all independent bids are lowered below the passive market maker’s bid, that bid must then be lowered when specified purchase limits are exceeded. Passive market making may cause the price of our common stock to be higher than the price that otherwise would exist in the open market in the absence of those transactions. The underwriters and dealers are not required to engage in passive market making and may end passive market making activities at any time.

Electronic Distribution

In connection with the offering, certain of the underwriters or securities dealers may distribute prospectuses by electronic means, such as e-mail.

Other Relationships

Some of the underwriters and their affiliates have engaged in, and may in the future engage in, investment banking and other commercial dealings in the ordinary course of business with us or our affiliates. They have received, or may in the future receive, customary fees and commissions for these transactions.

In addition, in the ordinary course of their business activities, the underwriters and their affiliates may make or hold a broad array of investments and actively trade debt and equity securities (or related derivative securities) and financial instruments (including bank loans) for their own account and for the accounts of their customers. Such investments and securities activities may involve securities and/or instruments of ours or our affiliates. The underwriters and their affiliates may also make investment recommendations and/or publish or express independent research views in respect of such securities or financial instruments and may hold, or recommend to clients that they acquire, long and/or short positions in such securities and instruments.

Notice to Prospective Investors in the European Economic Area

In relation to each Member State of the European Economic Area (each, a “Relevant Member State”), no offer of shares may be made to the public in that Relevant Member State other than:

(A)

to any legal entity which is a qualified investor as defined in the Prospectus Directive;

(B)

to fewer than 100 or, if the Relevant Member State has implemented the relevant provision of the 2010 PD Amending Directive, 150, natural or legal persons (other than qualified investors as defined in the Prospectus Directive), as permitted under the Prospectus Directive, subject to obtaining the prior consent of the representatives; or

(C)

in any other circumstances falling within Article 3(2) of the Prospectus Directive,

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provided that no such offer of shares shall require the Company or the representatives to publish a prospectus pursuant to Article 3 of the Prospectus Directive or supplement a prospectus pursuant to Article 16 of the Prospectus Directive.

Each person in a Relevant Member State who initially acquires any shares or to whom any offer is made will be deemed to have represented, acknowledged and agreed that it is a “qualified investor” within the meaning of the law in that Relevant Member State implementing Article 2(1)(e) of the Prospectus Directive. In the case of any shares being offered to a financial intermediary as that term is used in Article 3(2) of the Prospectus Directive, each such financial intermediary will be deemed to have represented, acknowledged and agreed that the shares acquired by it in the offer have not been acquired on a non-discretionary basis on behalf of, nor have they been acquired with a view to their offer or resale to, persons in circumstances which may give rise to an offer of any shares to the public other than their offer or resale in a Relevant Member State to qualified investors as so defined or in circumstances in which the prior consent of the representatives has been obtained to each such proposed offer or resale.

The Company, the representatives and their affiliates will rely upon the truth and accuracy of the foregoing representations, acknowledgements and agreements.

This prospectus supplement has been prepared on the basis that any offer of shares in any Relevant Member State will be made pursuant to an exemption under the Prospectus Directive from the requirement to publish a prospectus supplement for offers of shares. Accordingly any person making or intending to make an offer in that Relevant Member State of shares which are the subject of the offering contemplated in this prospectus supplement may only do so in circumstances in which no obligation arises for the Company or any of the underwriters to publish a prospectus pursuant to Article 3 of the Prospectus Directive in relation to such offer. Neither the Company nor the underwriters have authorized, nor do they authorize, the making of any offer of shares in circumstances in which an obligation arises for the Company or the underwriters to publish a prospectus for such offer.

For the purpose of the above provisions, the expression “an offer to the public” in relation to any shares in any Relevant Member State means the communication in any form and by any means of sufficient information on the terms of the offer and the shares to be offered so as to enable an investor to decide to purchase or subscribe the shares, as the same may be varied in the Relevant Member State by any measure implementing the Prospectus Directive in the Relevant Member State and the expression “Prospectus Directive” means Directive 2003/71/EC (including the 2010 PD Amending Directive, to the extent implemented in the Relevant Member States) and includes any relevant implementing measure in the Relevant Member State and the expression “2010 PD Amending Directive” means Directive 2010/73/EU.

Notice to Prospective Investors in the United Kingdom

In addition, in the United Kingdom, this document is being distributed only to, and is directed only at, and any offer subsequently made may only be directed at persons who are “qualified investors” (as defined in the Prospectus Directive)(i) who have professional experience in matters relating to investments falling within Article 19 (5) of the Financial Services and Markets Act 2000 (Financial Promotion) Order 2005, as amended (the “Order”) and/or (ii) who are high net worth companies (or persons to whom it may otherwise be lawfully communicated) falling within Article 49(2)(a) to (d) of the Order (all such persons together being referred to as “relevant persons”). This document must not be acted on or relied on in the United Kingdom by persons who are not relevant persons. In the United Kingdom, any investment or investment activity to which this document relates is only available to, and will be engaged in with, relevant persons.

Notice to Prospective Investors in Switzerland

The shares may not be publicly offered in Switzerland and will not be listed on the SIX Swiss Exchange (“SIX”) or on any other stock exchange or regulated trading facility in Switzerland. This document has been prepared without regard to the disclosure standards for issuance prospectuses under art. 652a or art. 1156 of the Swiss Code of Obligations or the disclosure standards for listing prospectuses under art. 27 ff. of the SIX Listing Rules or the listing rules of any other stock exchange or regulated trading facility in Switzerland. Neither this document nor any other offering or marketing material relating to the shares or the offering may be publicly distributed or otherwise made publicly available in Switzerland.

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Neither this document nor any other offering or marketing material relating to the offering, the Company, the shares have been or will be filed with or approved by any Swiss regulatory authority. In particular, this document will not be filed with, and the offer of shares will not be supervised by, the Swiss Financial Market Supervisory Authority FINMA (FINMA), and the offer of shares has not been and will not be authorized under the Swiss Federal Act on Collective Investment Schemes (“CISA”). The investor protection afforded to acquirers of interests in collective investment schemes under the CISA does not extend to acquirers of shares.

Notice to Prospective Investors in the Dubai International Financial Centre

This prospectus supplement relates to an Exempt Offer in accordance with the Offered Securities Rules of the Dubai Financial Services Authority (“DFSA”). This prospectus supplement is intended for distribution only to persons of a type specified in the Offered Securities Rules of the DFSA. It must not be delivered to, or relied on by, any other person. The DFSA has no responsibility for reviewing or verifying any documents in connection with Exempt Offers. The DFSA has not approved this prospectus supplement nor taken steps to verify the information set forth herein and has no responsibility for the prospectus supplement. The shares to which this prospectus supplement relates may be illiquid and/or subject to restrictions on their resale. Prospective purchasers of the shares offered should conduct their own due diligence on the shares. If you do not understand the contents of this prospectus supplement you should consult an authorized financial advisor.

Notice to Prospective Investors in Australia

No placement document, prospectus, product disclosure statement or other disclosure document has been lodged with the Australian Securities and Investments Commission (“ASIC”), in relation to the offering. This prospectus supplement does not constitute a prospectus, product disclosure statement or other disclosure document under the Corporations Act 2001 (the “Corporations Act”), and does not purport to include the information required for a prospectus, product disclosure statement or other disclosure document under the Corporations Act.

Any offer in Australia of the shares may only be made to persons (the “Exempt Investors”) who are “sophisticated investors” (within the meaning of section 708(8) of the Corporations Act), “professional investors” (within the meaning of section 708(11) of the Corporations Act) or otherwise pursuant to one or more exemptions contained in section 708 of the Corporations Act so that it is lawful to offer the shares without disclosure to investors under Chapter 6D of the Corporations Act.

The shares applied for by Exempt Investors in Australia must not be offered for sale in Australia in the period of 12 months after the date of allotment under the offering, except in circumstances where disclosure to investors under Chapter 6D of the Corporations Act would not be required pursuant to an exemption under section 708 of the Corporations Act or otherwise or where the offer is pursuant to a disclosure document which complies with Chapter 6D of the Corporations Act. Any person acquiring shares must observe such Australian on-sale restrictions.

This prospectus supplement contains general information only and does not take account of the investment objectives, financial situation or particular needs of any particular person. It does not contain any securities recommendations or financial product advice. Before making an investment decision, investors need to consider whether the information in this prospectus supplement is appropriate to their needs, objectives and circumstances, and, if necessary, seek expert advice on those matters.

Notice to Prospective Investors in Hong Kong

The shares have not been offered or sold and will not be offered or sold in Hong Kong, by means of any document, other than (a) to “professional investors” as defined in the Securities and Futures Ordinance (Cap. 571) of Hong Kong and any rules made under that Ordinance; or (b) in other circumstances which do not result in the document being a “prospectus” as defined in the Companies Ordinance (Cap. 32) of Hong Kong or which do not constitute an offer to the public within the meaning of that Ordinance. No advertisement, invitation or document relating to the shares has been or may be issued or has been or may be in the possession of any person for the purposes of issue, whether in Hong Kong or elsewhere, which is directed at, or the contents of which are likely to be accessed or read by, the public of Hong Kong (except if permitted to do so under the securities laws of Hong Kong) other than with respect to shares which are or are

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intended to be disposed of only to persons outside Hong Kong or only to “professional investors” as defined in the Securities and Futures Ordinance and any rules made under that Ordinance.

Notice to Prospective Investors in Japan

The shares have not been and will not be registered under the Financial Instruments and Exchange Law of Japan (Law No. 25 of 1948, as amended) and, accordingly, will not be offered or sold, directly or indirectly, in Japan, or for the benefit of any Japanese Person or to others for re-offering or resale, directly or indirectly, in Japan or to any Japanese Person, except in compliance with all applicable laws, regulations and ministerial guidelines promulgated by relevant Japanese governmental or regulatory authorities in effect at the relevant time. For the purposes of this paragraph, “Japanese Person” shall mean any person resident in Japan, including any corporation or other entity organized under the laws of Japan.

Notice to Prospective Investors in Singapore

This prospectus supplement has not been registered as a prospectus with the Monetary Authority of Singapore. Accordingly, this prospectus supplement and any other document or material in connection with the offer or sale, or invitation for subscription or purchase, of Non-CIS Securities may not be circulated or distributed, nor may the Non-CIS Securities be offered or sold, or be made the subject of an invitation for subscription or purchase, whether directly or indirectly, to persons in Singapore other than (i) to an institutional investor under Section 274 of the Securities and Futures Act, Chapter 289 of Singapore (the “SFA”), (ii) to a relevant person pursuant to Section 275(1), or any person pursuant to Section 275(1A), and in accordance with the conditions specified in Section 275, of the SFA, or (iii) otherwise pursuant to, and in accordance with the conditions of, any other applicable provision of the SFA.

Where the Non-CIS Securities are subscribed or purchased under Section 275 of the SFA by a relevant person which is:

(a)

a corporation (which is not an accredited investor (as defined in Section 4A of the SFA)) the sole business of which is to hold investments and the entire share capital of which is owned by one or more individuals, each of whom is an accredited investor; or

(b)

a trust (where the trustee is not an accredited investor) whose sole purpose is to hold investments and each beneficiary of the trust is an individual who is an accredited investor,

securities (as defined in Section 239(1) of the SFA) of that corporation or the beneficiaries’ rights and interest (howsoever described) in that trust shall not be transferred within six months after that corporation or that trust has acquired the Non-CIS Securities pursuant to an offer made under Section 275 of the SFA except:

(a)

to an institutional investor or to a relevant person defined in Section 275(2) of the SFA, or to any person arising from an offer referred to in Section 275(1A) or Section 276(4)(i)(B) of the SFA;

(b)

where no consideration is or will be given for the transfer;

(c)

where the transfer is by operation of law;

(d)

as specified in Section 276(7) of the SFA; or

(e)

as specified in Regulation 32 of the Securities and Futures (Offers of Investments) (Shares and Debentures) Regulations 2005 of Singapore.

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LEGAL MATTERS

Certain legal matters will be passed upon for us by Locke Lord LLP, Boston, Massachusetts. Stacie S. Aarestad, a partner of Locke Lord LLP, is our Assistant Secretary. Latham & Watkins LLP is counsel for the underwriters in connection with this offering.

EXPERTS

The financial statements and management’s assessment of the effectiveness of internal control over financial reporting (which is included in Management’s Report on Internal Control over Financial Reporting) incorporated in this prospectus by reference to the Annual Report on Form 10-K for the year ended December 31, 2014 have been so incorporated in reliance on the report of PricewaterhouseCoopers LLP, an independent registered public accounting firm, given on the authority of said firm as experts in auditing and accounting.

WHERE YOU CAN FIND MORE INFORMATION

This prospectus supplement and the accompanying prospectus are part of the registration statement on Form S-3 that we filed with the SEC under the Securities Act of 1933, as amended, and do not contain all the information set forth in the registration statement. Whenever a reference is made in this prospectus supplement or the accompanying prospectus to any of our contracts, agreements or other documents, the reference may not be complete, and you should refer to the exhibits that are a part of the registration statement or the exhibits to the reports or other documents incorporated by reference in this prospectus supplement and the accompanying prospectus for a copy of such contract, agreement or other document.

Because we are subject to the information and reporting requirements of the Securities Exchange Act of 1934, as amended, we file annual, quarterly and current reports, proxy statements and other information with the SEC. Our SEC filings are available to the public over the Internet at the SEC’s web site at http://www.sec.gov. You may also read and copy any document we file at the SEC’s Public Reference Room at 100 F Street, N.E., Washington, D.C. 20549. Please call the SEC at 1-800-SEC-0330 for further information on the operation of the Public Reference Room.

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INCORPORATION OF CERTAIN INFORMATION BY REFERENCE

The SEC allows us to “incorporate by reference” information from other documents that we file with them, which means that we can disclose important information to you by referring you to those documents. The information incorporated by reference is considered to be part of this prospectus supplement and the accompanying prospectus. Information contained in this prospectus supplement and the accompanying prospectus and information that we file with the SEC in the future and incorporate by reference in this prospectus supplement and the accompanying prospectus will automatically update and supersede this information. We incorporate by reference the documents listed below and any future filings we make with the SEC under Sections 13(a), 13(c), 14 or 15(d) of the Securities Exchange Act of 1934, as amended, until the termination of this offering; provided, however, that we are not incorporating any information furnished under Item 7.01 or Item 2.02 of any Current Report on Form 8-K:

•

our Annual Report on Form 10-K for the fiscal year ended December 31, 2014, filed with the SEC on February 27, 2015;

•

the portions of our Definitive Proxy Statement on Schedule 14A that are deemed “filed” with the SEC under the Securities Exchange Act of 1934, as amended, filed on April 24, 2014;

•

our Current Report on Form 8-K filed with the SEC on March 31, 2015 (solely with respect to Item 8.01); and

•

the description of our common stock contained in our registration statement on Form 8-A, filed with the SEC on August 2, 2000, which description thereof is contained in the prospectus included in our Registration Statement on Form S-1 (File No. 333-37394), including any amendment or reports filed for the purpose of updating such description.

You may request a copy of these filings, at no cost, by telephoning our Investor Relations department at (617) 225-2500 or writing us at:

Investor Relations
Dyax Corp.
55 Network Drive
Burlington, Massachusetts 01803

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[GRAPHIC MISSING]

Common stock
Preferred stock
Warrants
Debt Securities
Units

From time to time, we may offer and sell shares of common stock, preferred stock, warrants, debt securities and units, in amounts, at prices and on terms described in one or more supplements to this prospectus. This prospectus describes some of the general terms that may apply to an offering of such securities.

You should carefully read this prospectus and the prospectus supplements or term sheets relating to the specific issue of securities together with additional information described under the heading “Where You Can Find More Information” beginning on Page 22 of this prospectus before you decide to invest in any of these securities.

Our common stock is quoted on The NASDAQ Global Market under the symbol “DYAX”. On November 12, 2014, the last reported sale price for the common stock was $13.47 per share.

In this prospectus, “Dyax,” “we,” “us,” and “our” refer to Dyax Corp., excluding, unless the context otherwise requires, its subsidiaries.

These securities may be sold directly by us, through dealers or agents designated from time to time, to or through underwriters or through a combination of these methods. See “Plan of Distribution” beginning on Page 20 of this prospectus. We may also described the plan of distribution for any particular offering of these securities in any applicable prospectus supplement. If any agents, underwriters or dealers are involved in the sale of any securities in respect of which this prospectus is being delivered, we will disclose their names and the nature of our arrangements with them in a prospectus supplement. The net proceeds we expect to receive from any such sale will also be included in any prospectus supplement.

INVESTING IN OUR SECURITIES INVOLVES A HIGH DEGREE OF RISK. SEE “RISK FACTORS” ON PAGE 3.

NEITHER THE SECURITIES AND EXCHANGE COMMISSION NOR ANY STATE SECURITIES COMMISSION HAS APPROVED OR DISAPPROVED OF THESE SECURITIES OR PASSED UPON THE ADEQUACY OR ACCURACY OF THIS PROSPECTUS. ANY REPRESENTATION TO THE CONTRARY IS A CRIMINAL OFFENSE.

This prospectus may not be used to sell securities unless it is accompanied by a prospectus supplement.

Prospectus dated November 14, 2014.

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	Page
ABOUT THIS PROSPECTUS		1
DYAX CORP.		1
RISK FACTORS		3
FORWARD-LOOKING STATEMENTS		3
USE OF PROCEEDS		4
RATIO OF EARNINGS TO FIXED CHARGES AND RATIO OF COMBINED FIXED CHARGES AND PREFERRED STOCK DIVIDENDS TO EARNINGS		4
DESCRIPTION OF CAPITAL STOCK		5
DESCRIPTION OF DEBT SECURITIES		9
DESCRIPTION OF WARRANTS		16
DESCRIPTION OF UNITS		18
PLAN OF DISTRIBUTION		20
LEGAL MATTERS		22
EXPERTS		22
WHERE YOU CAN FIND MORE INFORMATION		22
INCORPORATION BY REFERENCE		23

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ABOUT THIS PROSPECTUS

This prospectus is part of an automatic shelf registration statement on Form S-3 that we filed with the Securities and Exchange Commission, or SEC, as a “well-known seasoned issuer” as defined in Rule 405 under the Securities Act of 1933, as amended. Under the shelf registration process, we may offer to sell any combination of the securities described in this prospectus, either individually or in units, in one or more offerings.

This prospectus provides you with a general description of the securities we may offer. Each time we offer a type or series of securities under this prospectus, we will provide a prospectus supplement that will contain more specific information about the terms of those securities. We also may authorize one or more free writing prospectuses to be provided to you that may contain material information relating to these offerings. We may also add, update or change in a prospectus supplement or free writing prospectus any of the information contained in this prospectus or in documents we have incorporated by reference into this prospectus. However, no prospectus supplement will fundamentally change the terms that are set forth in this prospectus or offer a security that is not registered and described in this prospectus at the time of its effectiveness. This prospectus, together with the applicable prospectus supplements, free writing prospectuses and the documents incorporated by reference into this prospectus, includes all material information relating to this offering. You should carefully read this prospectus, the applicable prospectus supplement and the additional information described under “Where You Can Find More Information” before buying securities in this offering.

You should rely only on the information we have provided or incorporated by reference in this prospectus, any prospectus supplement and any related free writing prospectus that we may authorize to be provided to you. We have not authorized anyone to provide you with information different from that contained or incorporated by reference in this prospectus. No dealer, salesperson or other person is authorized to give any information or to represent anything not contained or incorporated by reference in this prospectus. You must not rely on any unauthorized information or representation. This prospectus is an offer to sell only the securities offered hereby, but only under circumstances and in jurisdictions where it is lawful to do so. You should assume that the information in this prospectus, any prospectus supplement or related free writing prospectus is accurate only as of the date on the front of the document and that any information we have incorporated by reference is accurate only as of the date of the document incorporated by reference, regardless of the time of delivery of this prospectus or any sale of a security.

This prospectus contains summaries of certain provisions contained in some of the documents described herein, but reference is made to the actual documents for complete information. All of the summaries are qualified in their entirety by the actual documents. Copies of some of the documents referred to herein have been filed or will be filed as exhibits to the registration statement of which this prospectus is a part (or will be incorporated by reference from a current report on Form 8-K or quarterly report on Form 10-Q that we file with the SEC), and you may obtain copies of those documents as described below under “Where You Can Find More Information.”

DYAX CORP.

Dyax Corp.

We are a biopharmaceutical company focused on:

•

Hereditary Angioedema and Other Plasma-Kallikrein-Mediated Disorders

We develop and commercialize treatments for hereditary angioedema and are working to identify other disorders that are mediated by plasma kallikrein.

We discovered and developed KALBITOR, a plasma kallikrein inhibitor, and are selling it in the United States for the treatment of acute attacks of HAE. Additionally, we are developing DX-2930, a fully human monoclonal antibody inhibitor of plasma kallikrein, which we believe is a candidate to treat HAE prophylactically. The safety, tolerability, and kallikrein inhibition results of a Phase 1a clinical study in healthy volunteers supported the advancement of DX-2930 into a Phase 1b study in HAE patients that commenced in May 2014.

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We have also developed a biomarker assay that detects the activation of plasma kallikrein in patient blood. We intend to use this assay to expedite the development of DX-2930.

•

Licensing and Funded Research Portfolio (LFRP)

We have a portfolio of product candidates being developed by licensees using our phage display technology. This portfolio currently includes one approved product, CYRAMZA (ramucirumab) which is marketed by Eli Lilly and Company, and multiple product candidates in various stages of clinical development, including three in Phase 3 trials, for which we are eligible to receive future royalties and/or milestone payments.

Our History

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RISK FACTORS

An investment in our securities involves a high degree of risk. You should carefully consider the risk factors contained in a prospectus supplement as well as those set forth in our most recently filed periodic reports filed with the SEC, including our Annual Report on Form 10-K for the year ended December 31, 2013, as revised or supplemented by our quarterly reports on Form 10-Q, each of which are on file with the SEC and are incorporated by reference into this prospectus. Before making an investment decision, you should carefully consider these risks as well as other information we include or incorporate by reference in this prospectus or include in any applicable prospectus supplement. The risks described in these documents are not the only ones we face, but those that we consider to be material. There may be other unknown or unpredictable economic, business, competitive, regulatory or other factors that could have material adverse effects on our future results. Past financial performance may not be a reliable indicator of future performance, and historical trends should not be used to anticipate results or trends in future periods. If any of these risks actually occurs, our business, financial condition, results of operations or cash flow could be seriously harmed. This could cause the trading price of our common stock to decline, resulting in a loss of all or part of your investment. Please also read carefully the section below entitled “Forward-Looking Statements.”

FORWARD-LOOKING STATEMENTS

This prospectus and the documents incorporated by reference in this prospectus include forward-looking statements within the meaning of Section 27A of the Securities Act and Section 21E of the Securities Exchange Act of 1934, as amended. Any statement that is not a statement of historical fact should be considered a forward-looking statement. We often use words or phrases of expectation or uncertainty like “believe,” “anticipate,” “plan,” “expect,” “intent,” “project,” “future,” “may,” “will,” “could,” “would” and similar words to help identify forward-looking statements. Examples of forward-looking statements include statements regarding the potential benefits and usage of KALBITOR® (ecallantide) for treating HAE; the commercial potential of KALBITOR, including revenues and costs; prospects for clinical development of DX-2930 and other potential product candidates to address HAE and other PKM disorders; plans to enter into additional collaborative and licensing arrangements for ecallantide and for other compounds in development; the potential for marketing approval for KALBITOR in markets outside the United States; estimates of potential markets for our products and product candidates; prospects for future milestone payments and/or royalties with respect to licensee product candidates in our Licensing and Funded Research Portfolio (LFRP); the sufficiency of our cash, cash equivalents and short-term investments; the effect of the expiration of certain of our phage display patents under our LFRP; and expected future revenues, operating results and cash flows.

You should carefully read this entire prospectus and the documents incorporated by reference in this prospectus, particularly the section entitled “Risk Factors,” before you make an investment decision.

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USE OF PROCEEDS

Except as otherwise provided in the applicable prospectus supplement, we intend to use the net proceeds from the sale of the securities offered by this prospectus for general corporate purposes, which may include working capital, capital expenditures, commercialization and distribution expenditures, manufacturing expenditures, research and development expenditures, regulatory affairs expenditures, clinical trial expenditures, acquisitions of new technologies and investments, and the repayment, refinancing, redemption or repurchase of future indebtedness or capital stock. Additional information on the use of net proceeds from the sale of securities offered by this prospectus may be set forth in the prospectus supplement relating to that offering.

RATIO OF EARNINGS TO FIXED CHARGES AND RATIO OF COMBINED FIXED CHARGES AND PREFERRED STOCK DIVIDENDS TO EARNINGS

Our earnings have been insufficient to cover fixed charges and combined fixed charges and preferred stock dividends for each of the periods presented. The following table sets forth our ratio of earnings to fixed charges on a historical basis for the periods indicated. Because of the deficiency, ratio information is not applicable. For purposes of this calculation, “earnings” consist of net (loss) from continuing operations plus fixed charges. “Fixed charges” consist of the sum of interest expense and the component of rental expense believed by management to be representative of the interest factor for those amounts. Dollar amounts shown are in millions.


	Year Ended										Nine Months Ended September 30, 2014
	Dec. 31, 2009		Dec. 31, 2010		Dec. 31, 2011		Dec. 31, 2012		Dec. 31, 2013		Nine Months Ended September 30, 2014
Ratio of Earnings to Fixed Charges⁽¹⁾		—		—		—		—		—		—
Coverage Deficiency	$	62.4	$	24.5	$	34.6	$	29.3	$	27.8	$	9.6

(1)

We did not have any issued and outstanding preferred stock during the five year period ended December 31, 2012. We issued 41,418 shares of Series 1 Convertible Preferred Stock on May 15, 2013, all of which were converted to common stock on February 2014. No dividends were declared on such shares of preferred stock while they were outstanding and, consequently, our ratio of combined fixed charges and preference dividends to earnings is the same as our deficiency of earnings available to cover fixed charges. As of the date of this prospectus, there is no issued and outstanding preferred stock.

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DESCRIPTION OF CAPITAL STOCK

Our authorized capital stock currently consists of 200,000,000 shares of common stock, par value $0.01 per share, and 1,000,000 shares of preferred stock, $0.01 par value per share. Of our common stock, as of September 30, 2014, approximately 136,397,382 shares were issued and outstanding and an aggregate of approximately 12,236,459 shares were reserved for issuance under outstanding options and restricted stock units to purchase common stock.

The following summary of certain provisions of our common and preferred stock does not purport to be complete. You should refer to our amended and restated certificate of incorporation, as amended and supplemented to date, and our by-laws, included as exhibits to our most recent Annual Report on Form 10-K for the year ended December 31, 2013 or incorporated by reference into this prospectus. The summary below is also qualified by provisions of applicable law.

Common Stock

Holders of common stock are entitled to one vote per share on matters on which our stockholders vote. There are no cumulative voting rights. Holders of common stock are entitled to receive dividends, if declared by our board of directors, out of funds that we may legally use to pay dividends. If we liquidate or dissolve, holders of common stock are entitled to share ratably in our assets once our debts and any liquidation preference owed to any then-outstanding preferred stockholders are paid. All shares of common stock that are outstanding as of the date of this prospectus are fully-paid and nonassessable.

Preferred Stock

We are currently authorized to issue 1,000,000 shares of preferred stock, all of which remain undesignated. Our board of directors has the authority to issue such shares of preferred stock in one or more series and to fix the rights of such series. Our board will fix the designations, voting powers, preferences and rights of the preferred stock of each series, as well as the qualifications, limitations or restrictions thereof, in a certificate of designation relating to that series. We will file as an exhibit to the registration statement of which this prospectus is a part, or will incorporate by reference from reports that we file with the SEC, the form of any certificate of designation that describes the terms of the series of preferred stock we are offering before the issuance of that series of preferred stock. This description will include the following items, as applicable:

•

the title and stated value;

•

the number of shares we are offering;

•

the liquidation preference per share;

•

the purchase price;

•

the dividend rate, period and payment date and method of calculation for dividends;

•

whether dividends will be cumulative or non-cumulative and, if cumulative, the date from which dividends will accumulate;

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the procedures for any auction and remarketing, if any;

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the provisions for a sinking fund, if any;

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the provisions for redemption or repurchase, if applicable, and any restrictions on our ability to exercise those redemption and repurchase rights;

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any listing of the preferred stock on any securities exchange or market;

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whether the preferred stock will be convertible into our common stock, and, if applicable, the conversion price, or how it will be calculated, and the conversion period;

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whether the preferred stock will be exchangeable into debt securities, and, if applicable, the exchange price, or how it will be calculated, and the exchange period;

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voting rights, if any;

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preemptive rights, if any;

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restrictions on transfer, sale or other assignment, if any;

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whether interests in the preferred stock will be represented by depositary shares;

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a discussion of any material U.S. federal income tax considerations applicable to the preferred stock;

•

the relative ranking and preferences of the preferred stock as to dividend rights and rights if we liquidate, dissolve or wind up our affairs;

•

any limitations on the issuance of any class or series of preferred stock ranking senior to or on a parity with the series of preferred stock as to dividend rights and rights if we liquidate, dissolve or wind up our affairs; and

•

any other specific terms, preferences, rights or limitations of, or restrictions on, the preferred stock.

The General Corporation Law of the State of Delaware, our state of incorporation, provides that the holders of preferred stock will have the right to vote separately as a class (or, in some cases, as a series) on an amendment to our certificate of incorporation if the amendment would change the par value or, unless the certificate of incorporation provided otherwise, the number of authorized shares of the class or change the powers, preferences or special rights of the class or series so as to adversely affect the class or series, as the case may be. This right is in addition to any voting rights that may be provided for in the applicable certificate of designation.

We believe the power to issue preferred stock will provide our board of directors with flexibility in connection with certain possible corporate transactions. The issuance of preferred stock, however, could adversely affect the voting power of holders of our common stock, restrict their rights to receive payment upon liquidation, and have the effect of delaying, deferring, or preventing a change in control. We have no present plans to issue any shares of preferred stock.

Registration Rights

The holders of the shares of common stock issued upon conversion of all series of our former Class A convertible preferred stock were entitled to demand that we register those shares, known as registrable shares, under the Securities Act commencing one year after our initial public offering. Of those holders, only Henry Blair still has the ability to exercise this right because, as our Chairman of the Board, he remains an affiliate of the Company and, therefore, he may require us to file additional registration statements on Form S-3 for the sale of his registrable shares at any time if he is not then able to sell all of his shares under Rule 144. In addition, if we propose to register any more of our securities under the Securities Act, either for our own account or for the account of other security holders, he is entitled to notice of that further registration and to have his registrable shares included in it. These rights, however, are subject to conditions and limitations, including thresholds as to minimum values of shares required for a demand registration and the right of the underwriters of a registered offering of Dyax to limit the number of shares included in the offering. As a holder of registrable shares, Mr. Blair can require us to file the registration at our expense and, subject to some conditions and limitations, we are required to use our best efforts to effect the registration. Mr. Blair has waived his right to have his registrable shares registered under the Securities Act as part of this registration.

Dividend Policy

We have never declared or paid cash dividends on our capital stock. We currently intend to retain our future earnings, if any, for use in our business and therefore do not anticipate paying cash dividends in the foreseeable future. Payment of future dividends, if any, will be at the discretion of our board of directors after taking into account various factors, including our financial condition, operating results, current and anticipated cash needs and plans for expansion. In addition, our loan financing with HealthCare Royalty Partners puts restrictions on our ability to pay dividends.

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Delaware Anti-Takeover Law

Section 203 of the Delaware General Corporation Law is applicable to takeovers of Delaware corporations. Subject to exceptions enumerated in Section 203, Section 203 provides that a corporation shall not engage in any business combination with any “interested stockholder” for a three-year period following the date that the stockholder becomes an interested stockholder unless:

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prior to that date, the board of directors of the corporation approved either the business combination or the transaction that resulted in the stockholder becoming an interested stockholder;

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upon consummation of the transaction that resulted in the stockholder becoming an interested stockholder, the interested stockholder owned at least 85% of the voting stock of the corporation outstanding at the time the transaction commenced, though some shares may be excluded from the calculation; and

•

on or subsequent to that date, the business combination is approved by the board of directors of the corporation and by the affirmative votes of holders of at least two-thirds of the outstanding voting stock that is not owned by the interested stockholder.

Except as specified in Section 203, an interested stockholder is generally defined to include any person who, together with any affiliates or associates of that person, beneficially owns, directly or indirectly, 15% or more of the outstanding voting stock of the corporation, or is an affiliate or associate of the corporation and was the owner of 15% or more of the outstanding voting stock of the corporation, any time within three years immediately prior to the relevant date. Under certain circumstances, Section 203 makes it more difficult for an interested stockholder to effect various business combinations with a corporation for a three-year period, although the stockholders may elect not to be governed by this section, by adopting an amendment to the certificate of incorporation or by-laws, effective 12 months after adoption. Our amended and restated certificate of incorporation and by-laws do not opt out from the restrictions imposed under Section 203. We anticipate that the provisions of Section 203 may encourage companies interested in acquiring us to negotiate in advance with the board because the stockholder approval requirement would be avoided if a majority of the directors then in office excluding an interested stockholder approve either the business combination or the transaction that resulted in the stockholder becoming an interested stockholder. These provisions may have the effect of deterring hostile takeovers or delaying changes in control, which could depress the market price of our common stock and deprive stockholders of opportunities to realize a premium on shares of common stock held by them.

Charter and By-law Provisions

In addition to the board of directors’ ability to issue shares of preferred stock, our amended and restated certificate of incorporation, as amended and supplemented to date (“amended and restated certificate of incorporation”), and by-laws contain the following provisions that may have the effect of discouraging unsolicited acquisition proposals:

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our amended and restated certificate of incorporation classifies the board of directors into three classes with staggered three-year terms;

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our amended and restated certificate of incorporation include a provision prohibiting stockholder action by written consent;

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under our amended and restated certificate of incorporation and by-laws, our board of directors may enlarge the size of the board and fill the vacancies;

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our amended and restated certificate of incorporation requires the approval of 66 2/3% of the outstanding capital stock to merge the company into another entity, sell all or substantially all of our assets, or engage in any other business combination not approved by the board of directors;

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our amended and restated certificate of incorporation provides that some of its provisions may only be changed by an affirmative vote of 66 2/3% of our outstanding capital stock;

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our by-laws provide that a stockholder may not nominate candidates for the board of directors at any annual or special meeting unless that stockholder notifies us of its intention a specified period in advance and provides us with certain required information;

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our by-laws provide that special meetings of stockholders may only be called by the President, Chairman of the Board or by the board of directors; and

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stockholders who wish to bring business before the stockholders at our annual meeting must provide advance notice.

Transfer Agent and Registrar

The transfer agent and registrar for Dyax’s common stock is American Stock Transfer & Trust Company.

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DESCRIPTION OF DEBT SECURITIES

If we issue any debt securities offered by this prospectus and any accompanying prospectus supplement we will issue them under an indenture to be entered into by Dyax and a trustee to be identified in the applicable prospectus supplement. The terms of the debt securities will include those stated in the indenture and those made part of the indenture by reference to the Trust Indenture Act of 1939, as in effect on the date of the indenture. We have filed a copy of the proposed form of indenture as an exhibit to the registration statement in which this prospectus is included. Each indenture will be subject to and governed by the terms of the Trust Indenture Act of 1939.

Unless otherwise specified in the applicable prospectus supplement, the debt securities offered under this prospectus will represent direct, unsecured obligations of Dyax that will rank equally with all of our other unsecured indebtedness and will be effectively subordinated to all of our secured debts.

The following statements relating to the debt securities and the indenture are summaries and do not purport to be complete, and are subject in their entirety to the detailed provisions of the indenture.

General

We may issue the debt securities in one or more series with the same or various maturities, at par, at a premium, or at a discount. We will describe the particular terms of each series of debt securities in a prospectus supplement relating to that series, which we will file with the SEC. To review the terms of a series of debt securities, you must refer to both the prospectus supplement for the particular series and to the description of debt securities in this prospectus.

The prospectus supplement will set forth the following terms of the debt securities in respect of which this prospectus is delivered:

(1)

the title;

(2)

the aggregate principal amount;

(3)

the issue price or prices (expressed as a percentage of the aggregate principal amount thereof);

(4)

any limit on the aggregate principal amount;

(5)

the date or dates on which principal is payable;

(6)

the interest rate or rates (which may be fixed or variable) or, if applicable, the method used to determine the rate or rates;

(7)

the date or dates from which the interest, if any, will be payable and any regular record date for the interest payable;

(8)

the place or places where principal and, if applicable, premium and interest, is payable;

(9)

the terms and conditions upon which Dyax may, or the holders may require Dyax to, redeem or repurchase the debt securities;

(10)

the denominations in which the debt securities may be issuable, if other than denominations of $1,000 or any integral multiple thereof;

(11)

whether the debt securities are to be issuable in the form of certificated debt securities (as described below) or global debt securities (as described below);

(12)

the portion of principal amount that will be payable upon declaration of acceleration of the maturity date if other than the principal amount of the debt securities;

(13)

the currency of denomination;

(14)

the designation of the currency, currencies or currency units in which payment of principal and, if applicable, premium and interest, will be made;

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(15)

if payments of principal and, if applicable, premium or interest, on the debt securities are to be made in one or more currencies or currency units other than the currency of denomination, the manner in which the exchange rate with respect to these payments will be determined;

(16)

if amounts of principal and, if applicable, premium and interest may be determined (a) by reference to an index based on a currency or currencies other than the currency of denomination or designation or (b) by reference to a commodity, commodity index, stock exchange index or financial index, then the manner in which these amounts will be determined;

(17)

the provisions, if any, relating to any security provided for the debt securities;

(18)

any addition to or change in the covenants and/or the acceleration provisions described in this prospectus or in the indenture;

(19)

any events of default;

(20)

the terms and conditions for conversion into or exchange for shares of common stock or preferred stock;

(21)

any other terms, which may modify or delete any provision of the indenture insofar as it applies to that series;

(22)

any depositaries, interest rate calculation agents, exchange rate calculation agents or other agents; and

(23)

the terms and conditions, if any, upon which the debt securities shall be subordinated in right of payment to other indebtedness of Dyax.

We may issue discount debt securities that provide for an amount less than the stated principal amount to be due and payable upon acceleration of the maturity of the debt securities in accordance to the terms of the indenture. We may also issue debt securities in bearer form, with or without coupons. If we issue discount securities or debt securities in bearer form, we will describe United States federal income tax considerations and other special considerations that apply to the debt securities in the applicable prospectus supplement.

We may issue debt securities denominated in or payable in a foreign currency or currencies or a foreign currency unit or units. If we do so, we will describe the restrictions, elections, general tax considerations, specific terms and other information with respect to the issue of debt securities and the foreign currency or currencies or foreign currency unit or units in the applicable prospectus supplement.

Exchange and/or Conversion Rights

If we issue debt securities that may be exchanged for or converted into shares of common stock or preferred stock, we will describe the terms of exchange or conversion in the prospectus supplement relating to those debt securities.

Transfer and Exchange

We may issue debt securities that will be represented by either:

(1)

“book-entry securities,” which means that there will be one or more global securities registered in the name of The Depository Trust Company, as depository, or a nominee of the depository; or

(2)

“certificated securities,” which means that they will be represented by a certificate issued in definitive registered form.

We will specify in the prospectus supplement applicable to a particular offering whether the debt securities offered will be book-entry or certificated securities. Except as set forth under “— Global Debt Securities and Book Entry System” below, book-entry debt securities will not be issuable in certificated form.

Certificated Debt Securities

If you hold certificated debt securities that have been offered by this prospectus, you may transfer or exchange them at the trustee’s office or at the paying agency in accordance with the terms of the indenture.

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You will not be charged a service charge for any transfer or exchange of certificated debt securities, but may be required to pay an amount sufficient to cover any tax or other governmental charge payable in connection with the transfer or exchange.

You may effect the transfer of certificated debt securities and of the right to receive the principal of, premium, and/or interest, if any, on your certificated debt securities only by surrendering the certificate representing your certificated debt securities and having us or the trustee issue a new certificate to the new holder.

Global Debt Securities and Book-Entry System

If we decided to issue debt securities in the form of one or more global securities, then we will register the global securities in the name of the depository for the global securities or in the nominee of the depository, and the global securities will be delivered by the trustee to the depository for credit to the accounts of the holders of beneficial interest in the debt securities. Each global security will:

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be registered in the name of a depositary, or its nominee, that we will identify in a prospectus supplement;

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be deposited with the depositary or nominee or custodian; and

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bear any required legends.

No global security may be exchanged in whole or in part for debt securities registered in the name of any person other than the depositary or any nominee unless:

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the depositary has notified us that it is unwilling or unable to continue as depositary or has ceased to be qualified to act as depositary;

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an event of default has occurred and is continuing with respect to the debt securities of the applicable series; or

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any other circumstance described in a prospectus supplement has occurred permitting or requiring the issuance of any such security.

As long as the depositary, or its nominee, is the registered owner of a global security, the depositary or nominee will be considered the sole owner and holder of the debt securities represented by the global security for all purposes under the indentures. Except in the above limited circumstances, owners of beneficial interests in a global security will not be:

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entitled to have the debt securities registered in their names;

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entitled to physical delivery of certificated debt securities; or

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considered to be holders of those debt securities under the indenture.

Payments on a global security will be made to the depositary or its nominee as the holder of the global security. Some jurisdictions have laws that require that certain purchasers of securities take physical delivery of such securities in definitive form. These laws may impair the ability to transfer beneficial interests in a global security.

Institutions that have accounts with the depositary or its nominee are referred to as “participants.” Ownership of beneficial interests in a global security will be limited to participants and to persons that may hold beneficial interests through participants. The depositary will credit, on its book-entry registration and transfer system, the respective principal amounts of debt securities represented by the global security to the accounts of its participants.

Ownership of beneficial interests in a global security will be shown on and effected through records maintained by the depositary, with respect to participants’ interests, or any participant, with respect to interests of persons held by participants on their behalf.

Payments, transfers and exchanges relating to beneficial interests in a global security will be subject to policies and procedures of the depositary. The depositary policies and procedures may change from time to

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time. Neither any trustee nor we will have any responsibility or liability for the depositary’s or any participant’s records with respect to beneficial interests in a global security.

The prospectus supplement will describe the specific terms of the depository arrangement for debt securities of a series that are issued in global form. Dyax and its agents, the trustee, and any of its agents will not have any responsibility or liability for any aspect of the records relating to or payments made on account of beneficial ownership interests in the global debt security or for maintaining, supervising or reviewing any records relating to the beneficial ownership interests.

No Protection in the Event of Change of Control

The indenture does not have any covenants or other provisions providing for a put or increased interest or otherwise that would afford holders of debt securities additional protection in the event of a recapitalization transaction, a change of control of Dyax or a highly leveraged transaction. If we offer any covenants of this type or provisions with respect to any debt securities in the future, we will describe them in the applicable prospectus supplement.

Covenants

Unless otherwise indicated in this prospectus or a prospectus supplement, the debt securities will not have the benefit of any covenants that limit or restrict our business or operations, the pledging of our assets or the incurrence by us of indebtedness. We will describe in the applicable prospectus supplement any material covenants of a series of debt securities.

Consolidation, Merger and Sale of Assets

We have agreed in the indenture that we will not consolidate with or merge into any other person or convey, transfer, sell or lease our properties and assets substantially as an entirety to any person, unless:

(1)

the person formed by the consolidation or into or with which we are merged or the person to which our properties and assets are conveyed, transferred, sold or leased, is a corporation organized and existing under the laws of the United States, any State thereof or the District of Columbia and, if we are not the surviving person, the surviving person has expressly assumed all of our obligations, including the payment of the principal of and, premium, if any, and interest on the debt securities and the performance of the other covenants under the indenture; and

(2)

immediately after giving effect to the transaction, no event of default, and no event which, after notice or lapse of time or both, would become an event of default, has occurred and is continuing under the indenture.

Events of Default

Unless otherwise specified in the applicable prospectus supplement, the following events will be events of default under the indenture with respect to debt securities of any series:

(1)

we fail to pay any principal of, or premium, if any, when it becomes due;

(2)

we fail to pay any interest within 45 days after it becomes due;

(3)

we fail to observe or perform any other covenant in the debt securities or the indenture for 45 days after written notice from the trustee or the holders of not less than 25% in aggregate principal amount of the outstanding debt securities of that series; and

(4)

certain events occur involving bankruptcy, insolvency or reorganization of Dyax or any of our significant subsidiaries.

The trustee may withhold notice to the holders of the debt securities of any series of any default, except in payment of principal or premium, if any, or interest on the debt securities of that series, if the trustee considers it to be in the best interest of the holders of the debt securities of that series to do so.

If an event of default (other than an event of default resulting from certain events of bankruptcy, insolvency or reorganization) occurs, and is continuing, then the trustee or the holders of not less than 25% in aggregate principal amount of the outstanding debt securities of any series may accelerate the maturity of the debt securities.

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If this happens, the entire principal amount of all the outstanding debt securities of that series plus accrued interest to the date of acceleration will be immediately due and payable. At any time after an acceleration, but before a judgment or decree based on the acceleration is obtained by the trustee, the holders of a majority in aggregate principal amount of outstanding debt securities of that series may rescind and annul the acceleration if (1) all events of default (other than nonpayment of accelerated principal, premium or interest) have been cured or waived, (2) all overdue interest and overdue principal has been paid and (3) the rescission would not conflict with any judgment or decree.

If an event of default resulting from certain events of bankruptcy, insolvency or reorganization occurs, the principal, premium and interest amount with respect to all of the debt securities of any series shall be due and payable immediately without any declaration or other act on the part of the trustee or the holders of the debt securities of that series.

The holders of a majority in principal amount of the outstanding debt securities of a series shall have the right to waive any existing default or compliance with any provision of the indenture or the debt securities of that series and to direct the time, method and place of conducting any proceeding for any remedy available to the trustee, subject to certain limitations specified in the indenture.

No holder of any debt security of a series will have any right to institute any proceeding with respect to the indenture or for any remedy under the indenture, unless:

(1)

the holder gives to the trustee written notice of a continuing event of default;

(2)

the holders of at least 25% in aggregate principal amount of the outstanding debt securities of that series make a written request and offer reasonable indemnity to the trustee to institute proceeding as a trustee;

(3)

the trustee fails to institute proceeding within 60 days of the request; and

(4)

the holders of a majority in aggregate principal amount of the outstanding debt securities of that series do not give the trustee a direction inconsistent with their request during the 60-day period.

However, these limitations do not apply to a suit instituted for payment on debt securities of any series on or after the due dates expressed in the debt securities.

Modification and Waiver

From time to time, we and the trustee may, without the consent of holders of the debt securities of one or more series, amend the indenture or the debt securities of one or more series, or supplement the indenture, for certain specified purposes, including:

(1)

to provide that the surviving entity following a change of control of Dyax permitted under the indenture shall assume all of our obligations under the indenture and debt securities;

(2)

to provide for uncertificated debt securities in addition to certificated debt securities;

(3)

to comply with any requirements of the SEC under the Trust Indenture Act of 1939;

(4)

to cure any ambiguity, defect or inconsistency, or make any other change that does not adversely affect the rights of any holder;

(5)

provide for the issuance of and establish the form and terms and conditions of debt securities of any series as permitted by the underwriter; and

(6)

to appoint a successor trustee under the indenture with respect to one or more series.

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From time to time we and the trustee may, with the consent of holders of at least a majority in principal amount of the outstanding debt securities, amend or supplement the indenture or the debt securities, or waive compliance in a particular instance by us with any provision of the indenture or the debt securities; but without the consent of each holder affected by the action, we may not modify or supplement the indenture or the debt securities or waive compliance with any provision of the indenture or the debt securities in order to:

(1)

reduce the amount of debt securities whose holders must consent to an amendment, supplement, or waiver to the indenture or the debt security;

(2)

reduce the rate of or change the time for payment of interest;

(3)

reduce the principal of or premium on or change the stated maturity;

(4)

make any debt security payable in money other than that stated in the debt security;

(5)

change the amount or time of any payment required or reduce the premium payable upon any redemption, or change the time before which no redemption of this type may be made;

(6)

waive a default on the payment of the principal of, interest on, or redemption payment; and

(7)

take any other action otherwise prohibited by the indenture to be taken without the consent of each holder affected by that action.

Defeasance and Discharge of Debt Securities and Certain Covenants in Certain Circumstances

The indenture permits us, at any time, to elect to discharge our obligations with respect to one or more series of debt securities by following certain procedures described in the indenture. These procedures will allow us either:

(1)

to defease and be discharged from any and all of our obligations with respect to any debt securities except for the following obligations (which discharge is referred to as “legal defeasance”):

(a)

to register the transfer or exchange of the debt securities;

(b)

to replace temporary or mutilated, destroyed, lost or stolen debt securities;

(c)

to compensate and indemnify the trustee; or

(d)

to maintain an office or agency in respect of the debt securities and to hold monies for payment in trust; or

(2)

to be released from our obligations with respect to the debt securities under certain covenants contained in the indenture, as well as any additional covenants which may be contained in the applicable prospectus supplement (which release is referred to as “covenant defeasance”).

In order to exercise either defeasance option, we must deposit with the trustee or other qualifying trustee, in trust for this purpose:

(1)

money;

(2)

U.S. Government Obligations (as described below) or Foreign Government Obligations (as described below) which through the scheduled payment of principal and interest in accordance with their terms will provide money; or

(3)

a combination of money and/or U.S. Government Obligations and/or Foreign Government Obligations sufficient in the written opinion of a nationally-recognized firm of independent accountants to provide money;

which in each case specified in clauses (1) through (3) above, provides a sufficient amount to pay the principal of, premium, if any, and interest, if any, on the debt securities of a series, on the scheduled due dates or on a selected date of redemption in accordance with the terms of the indenture.

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In addition, defeasance may be effected only if, among other things:

(1)

in the case of either legal or covenant defeasance, we deliver to the trustee an opinion of counsel, as specified in the indenture, stating that as a result of the defeasance neither the trust nor the trustee will be required to register as an investment company under the Investment Company Act of 1940;

(2)

in the case of legal defeasance, we deliver to the trustee an opinion of counsel stating that we have received from, or there has been published by, the Internal Revenue Service a ruling to the effect that, or there has been a change in any applicable federal income tax law with the effect that, and the opinion shall confirm that, the holders of outstanding debt securities will not recognize income, gain or loss for United States federal income tax purposes solely as a result of the legal defeasance and will be subject to United States federal income tax on the same amounts, in the same manner, including as a result of prepayment, and at the same times as would have been the case if a defeasance had not occurred;

(3)

in the case of covenant defeasance, we deliver to the trustee an opinion of counsel to the effect that the holders of the outstanding debt securities will not recognize income, gain or loss for United States federal income tax purposes as a result of the covenant defeasance and will be subject to United States federal income tax on the same amounts, in the same manner and at the same times as would have been the case if a covenant defeasance had not occurred; and

(4)

certain other conditions described in the indenture are satisfied.

If we fail to comply with our remaining obligations under the indenture and applicable supplemental indenture after a covenant defeasance of the indenture and applicable supplemental indenture, and the debt securities are declared due and payable because of the occurrence of any undefeased event of default, the amount of money and/or U.S. Government Obligations and/or Foreign Government Obligations on deposit with the trustee could be insufficient to pay amounts due under the debt securities of that series at the time of acceleration. We will, however, remain liable in respect of these payments.

The term “U.S. Government Obligations” as used in the above discussion means securities which are direct obligations of or non-callable obligations guaranteed by the United States of America for the payment of which obligation or guarantee the full faith and credit of the United States of America is pledged.

The term “Foreign Government Obligations” as used in the above discussion means, with respect to debt securities of any series that are denominated in a currency other than U.S. dollars (1) direct obligations of the government that issued or caused to be issued the currency for the payment of which obligations its full faith and credit is pledged or (2) obligations of a person controlled or supervised by or acting as an agent or instrumentality of that government the timely payment of which is unconditionally guaranteed as a full faith and credit obligation by that government, which in either case under clauses (1) or (2), are not callable or redeemable at the option of the issuer.

Regarding the Trustee

We will identify the trustee with respect to any series of debt securities in the prospectus supplement relating to the debt securities. You should note that if the trustee becomes a creditor of Dyax, the indenture and the Trust Indenture Act of 1939 limit the rights of the trustee to obtain payment of claims in certain cases, or to realize on certain property received in respect of certain claims, as security or otherwise. The trustee and its affiliates may engage in, and will be permitted to continue to engage in, other transactions with us and our affiliates. If, however, the trustee, acquires any “conflicting interest” within the meaning of the Trust Indenture Act of 1939, it must eliminate the conflict or resign.

The holders of a majority in principal amount of the then outstanding debt securities of any series may direct the time, method and place of conducting any proceeding for exercising any remedy available to the trustee. If an event of default occurs and is continuing, the trustee, in the exercise of its rights and powers, must use the degree of care and skill of a prudent person in the conduct of his or her own affairs. Subject to this provision, the trustee will be under no obligation to exercise any of its rights or powers under the indenture at the request of any of the holders of the debt securities, unless they have offered to the trustee reasonable indemnity or security.

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DESCRIPTION OF WARRANTS

General

We may issue warrants to purchase debt securities (which we refer to as debt warrants), preferred stock (which we refer to as preferred stock warrants) or common stock (which we refer to as common stock warrants). Any of these warrants may be issued independently or together with any other securities offered by this prospectus and may be attached to or separate from the other securities. If warrants are issued, they will be issued under warrant agreements to be entered into between us and a bank or trust company, as warrant agent, all of which will be described in the prospectus supplement relating to the warrants being offered.

Debt Warrants

We will describe the terms of debt warrants offered in the applicable prospectus supplement, the warrant agreement relating to the debt warrants and the debt warrant certificates representing the debt warrants, including the following:

(1)

the title;

(2)

the aggregate number offered;

(3)

their issue price or prices;

(4)

the designation, aggregate principal amount and terms of the debt securities purchasable upon exercise, and the procedures and conditions relating to exercise;

(5)

the designation and terms of any related debt securities and the number of debt warrants issued with each security;

(6)

the date, if any, on and after which the debt warrants and the related debt securities will be separately transferable;

(7)

the principal amount of debt securities purchasable upon exercise, and the price at which that principal amount of debt securities may be purchased upon exercise;

(8)

the commencement and expiration dates of the right to exercise;

(9)

the maximum or minimum number which may be exercised at any time;

(10)

a discussion of the material United States federal income tax considerations applicable to exercise; and

(11)

any other terms, procedures and limitations relating to exercise.

Debt warrant certificates will be exchangeable for new debt warrant certificates of different denominations, and debt warrants may be exercised at the corporate trust office of the warrant agent or any other office indicated in the applicable prospectus supplement. Before exercising their debt warrants, holders will not have any of the rights of holders of the securities purchasable upon exercise and will not be entitled to payments of principal of, or premium, if any, or interest, if any, on the securities purchasable upon exercise.

Other Warrants

The applicable prospectus supplement will describe, where applicable, the following terms and other information relating to the preferred stock warrants or common stock warrants offered under this prospectus:

(1)

the title;

(2)

the securities issuable upon exercise;

(3)

the issue price or prices;

(4)

the number of warrants issued with each share of preferred stock or common stock;

(5)

any provisions for adjustment of (a) the number or amount of shares of preferred stock or common stock receivable upon exercise of the warrants or (b) the exercise price;

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(6)

if applicable, the date on and after which the warrants and the related preferred stock or common stock will be separately transferable;

(7)

if applicable, a discussion of the material United States federal income tax considerations applicable to the exercise of the warrants;

(8)

any other terms, including terms, procedures and limitations relating to exchange and exercise;

(9)

the commencement and expiration dates of the right to exercise; and

(10)

the maximum or minimum number that may be exercised at any time.

Exercise of Warrants

Each warrant will entitle the holder to purchase for cash the principal amount of debt securities or shares of preferred stock or common stock at the applicable exercise price set forth in, or determined as described in, the applicable prospectus supplement. Warrants may be exercised at any time up to the close of business on the expiration date set forth in the applicable prospectus supplement. After the close of business on the expiration date, unexercised warrants will become void.

Warrants may be exercised by delivering to the corporation trust office of the warrant agent or any other officer indicated in the applicable prospectus supplement (a) the warrant certificate properly completed and duly executed and (b) payment of the amount due upon exercise. As soon as practicable following exercise, we will forward the debt securities or shares of preferred stock or common stock purchasable upon exercise. If less than all of the warrants represented by a warrant certificate are exercised, a new warrant certificate will be issued for the remaining warrants.

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DESCRIPTION OF UNITS

The following description, together with the additional information we may include in any applicable prospectus supplements, summarizes the material terms and provisions of the units that we may offer under this prospectus. Units may be offered independently or together with common stock, preferred stock, debt securities and/or warrants offered by any prospectus supplement, and may be attached to or separate from those securities. While the terms we have summarized below will apply generally to any units that we may offer under this prospectus, we will describe the particular terms of any series of units in more detail in the applicable prospectus supplement. The terms of any units offered under a prospectus supplement may differ from the terms described below. However, no prospectus supplement will fundamentally change the terms that are set forth in this prospectus or offer a security that is not registered and described in this prospectus at the time of its effectiveness.

We will issue the units under a unit agreement and use the term “unit agreement” to refer to any such agreement.

We will file as exhibits to the registration statement of which this prospectus is a part, or will incorporate by reference from a current report on Form 8-K that we file with the SEC, the form of unit agreement that describes the terms of the series of units we are offering, and any supplemental agreements, before the issuance of the related series of units. The following summaries of material terms and provisions of the units are subject to, and qualified in their entirety by reference to, all the provisions of the unit agreement and any supplemental agreements applicable to a particular series of units. We urge you to read the applicable prospectus supplements related to the particular series of units that we sell under this prospectus, as well as the complete unit agreement and any supplemental agreements that contain the terms of the units.

General

We may issue units comprised of one or more debt securities, shares of common stock, shares of preferred stock and warrants in any combination. Each unit will be issued so that the holder of the unit is also the holder of each security included in the unit. Thus, the holder of a unit will have the rights and obligations of a holder of each included security. The unit agreement under which a unit is issued may provide that the securities included in the unit may not be held or transferred separately, at any time or at any time before a specified date.

We will describe in the applicable prospectus supplement the terms of the series of units, including:

•

the designation and terms of the units and of the securities comprising the units, including whether and under what circumstances those securities may be held or transferred separately;

•

any provisions of the governing unit agreement that differ from those described below; and

•

any provisions for the issuance, payment, settlement, transfer or exchange of the units or of the securities comprising the units.

The provisions described in this section, as well as those described under “Description of Capital Stock,” “Description of Debt Securities” and “Description of Warrants” will apply to each unit and to any common stock, preferred stock, debt security or warrant included in each unit, respectively.

Issuance in Series

We may issue units in such amounts and in numerous distinct series as we determine.

Enforceability of Rights by Holders of Units

Each unit agent will act solely as our agent under the applicable unit agreement and will not assume any obligation or relationship of agency or trust with any holder of any unit. A single bank or trust company may act as unit agent for more than one series of units. A unit agent will have no duty or responsibility in case of any default by us under the applicable unit agreement or unit, including any duty or responsibility to initiate any proceedings at law or otherwise, or to make any demand upon us. Any holder of a unit may, without the consent of the related unit agent or the holder of any other unit, enforce by appropriate legal action its rights as holder under any security included in the unit.

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Title

Dyax, the unit agent and any of their agents may treat the registered holder of any unit certificate as an absolute owner of the units evidenced by that certificate for any purposes and as the person entitled to exercise the rights attaching to the units so requested, despite any notice to the contrary.

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PLAN OF DISTRIBUTION

We may sell the securities being offered by us in this prospectus:

(1)

directly to purchasers;

(2)

through agents;

(3)

through dealers;

(4)

through underwriters; or

(5)

through a combination of any of these methods of sale.

We and our agents and underwriters may sell the securities being offered by us in this prospectus from time to time in one or more transactions:

(1)

at a fixed price or prices, which may be changed;

(2)

at market prices prevailing at the time of sale;

(3)

at prices related to the prevailing market prices; or

(4)

at negotiated prices.

Direct Sales Through Agents

We may solicit directly offers to purchase securities. We may also designate agents from time to time to solicit offers to purchase securities. Any agent, who may be deemed to be an “underwriter” as that term is defined in the Securities Act of 1933, may then resell the securities to the public at varying prices to be determined by that agent at the time of resale.

Sales Through Underwriters or Dealers

If we use underwriters to sell securities, we will enter into an underwriting agreement with them at the time of the sale to them. The names of the underwriters will be set forth in the prospectus supplement that will be used by them together with this prospectus to make resales of the securities to the public. In connection with the sale of the securities offered, these underwriters may be deemed to have received compensation from us in the form of underwriting discounts or commissions. Underwriters may also receive commissions from purchasers of the securities.

Underwriters may also use dealers to sell securities. If this happens, these dealers may receive compensation in the form of discounts, concessions or commissions from the underwriters and/or commissions from the purchasers for whom they may act as agents.

Any underwriting compensation paid by us to underwriters in connection with the offering of the securities offered in this prospectus, and any discounts, concessions or commissions allowed by underwriters to participating dealers, will be set forth in the applicable prospectus supplement. In no event will the total amount of compensation paid to any member of The Financial Industry Regulatory Authority (FINRA) upon completion of any offering exceed 8.0% of the maximum gross proceeds of such offering.

Underwriters, dealers, agents and other persons may be entitled, under agreements that may be entered into with us, to indemnification by us against certain civil liabilities, including liabilities under the Securities Act of 1933, or to contribution with respect to payments that they may be required to make in respect of these liabilities. Underwriters and agents may engage in transactions with, or perform services for, us in the ordinary course of business.

If so indicated in the applicable prospectus supplement, we will authorize underwriters, dealers, or other persons to solicit offers by certain institutions to purchase the securities offered by us under this prospectus pursuant to contracts providing for payment and delivery on a future date or dates. The obligations of any purchaser under any these contracts will be subject only to those conditions described in the applicable prospectus supplement, and the prospectus supplement will set forth the price to be paid for securities pursuant to these contracts and the commissions payable for solicitation of these contracts.

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Any underwriter may engage in over-allotment, stabilizing and syndicate short covering transactions and penalty bids only in compliance with Regulation M of the Securities Exchange Act of 1934. If we offer securities in an “at the market” offering, stabilizing transactions will not be permitted. Over-allotment involves sales in excess of the offering size, which creates a short position. Stabilizing transactions involve bids to purchase the underlying security so long as the stabilizing bids do not exceed a specified maximum. Syndicate short covering transactions involve purchases of securities in the open market after the distribution has been completed in order to cover syndicate short positions. Penalty bids permit the underwriters to reclaim selling concessions from dealers when the securities originally sold by the dealers are purchased in covering transactions to cover syndicate short positions. These transactions may cause the price of the securities sold in an offering to be higher than it would otherwise be. These transactions, if commenced, may be discontinued by the underwriters at any time.

Rights Offerings

We may offer rights to our existing stockholders to purchase additional common shares of ours. For any particular subscription rights, the applicable prospectus supplement will describe the terms of such rights, including the period during which such rights may be exercised, the manner of exercising such rights, the transferability of such rights and the number of common shares that may be purchased in connection with each right and the subscription price for the purchase of such common shares. In connection with a rights offering, we may enter into a separate agreement with one or more underwriters or standby purchasers to purchase any of our common shares not subscribed for in the rights offering by existing stockholders, which will be described in the applicable prospectus supplement.

General Information

Each series of securities offered under this prospectus will be a new issue with no established trading market, other than the common stock, which is listed on The Nasdaq Global Market. Any shares of common stock sold pursuant to a prospectus supplement will be listed on The Nasdaq Global Market, subject to official notice of issuance. Any underwriters to whom we sell securities for public offering and sale may make a market in the securities, but these underwriters will not be obligated to do so and may discontinue any market making at any time without notice. We may elect to list any of the securities we may offer from time to time for trading on an exchange or on The Nasdaq Global Market, but we are not obligated to do so.

The anticipated date of delivery of the securities offered hereby will be set forth in the applicable prospectus supplement relating to each offering.

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LEGAL MATTERS

The validity of the common stock offered hereby will be passed upon by Edwards Wildman Palmer LLP, Boston, Massachusetts, our counsel. Stacie S. Aarestad, a partner of Edwards Wildman Palmer LLP, is our Assistant Secretary.

EXPERTS

The financial statements and management’s assessment of the effectiveness of internal control over financial reporting (which is included in Management’s Report on Internal Control over Financial Reporting) incorporated in this prospectus by reference to the Annual Report on Form 10-K for the year ended December 31, 2013 have been so incorporated in reliance on the report of PricewaterhouseCoopers LLP, an independent registered public accounting firm, given on the authority of said firm as experts in auditing and accounting.

WHERE YOU CAN FIND MORE INFORMATION

We file annual, quarterly and special reports, proxy statements and other information with the SEC. Our internet website is www.dyax.com and through the Investors section of our website, you may access, free of charge, our filings, as soon as reasonably practicable after we electronically file such materials with, or furnish them to, the SEC. The information contained in our website is not incorporated by reference into this prospectus and does not constitute a part of this prospectus. You may also read and copy any document we file at the SEC’s Public Reference Room at 100 F Street, N.E., Washington, D.C. 20549. Copies of all or a portion of such materials can be obtained from the Public Reference Section of the SEC upon payment of prescribed fees. Please call the SEC at 1-800-SEC-0330 for further information. Our SEC filings are also available to the public at the SEC’s web site at http://www.sec.gov. Our common stock is listed on The NASDAQ Global Market. Reports and other information concerning us can be inspected at the offices of The NASDAQ Global Market.

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INCORPORATION BY REFERENCE

The SEC allows us to “incorporate by reference” the information we have filed with them, which means that we can disclose important information to you by referring you to those documents. The information incorporated by reference is deemed to be a part of this prospectus. The reports and other documents we file after the date of this prospectus will update, supplement and supersede the information in this prospectus. We incorporate by reference the documents listed below and any documents we file subsequently with the SEC under Section 13(a), 13(c), 14, or 15(d) of the Exchange Act after the date of the initial registration statement and prior to the effectiveness of the registration statement and after the date of the prospectus and prior to the termination of the offering; provided, however, that we are not incorporating any information furnished under Item 2.02 or Item 7.01 of any Current Report on Form 8-K.

•

our Annual Report on Form 10-K for the fiscal year ended December 31, 2013, filed with the SEC on March 3, 2014;

•

our Quarterly Report on Form 10-Q for the quarter ended March 31, 2014, filed with the SEC on May 2, 2014, our Quarterly Report on Form 10-Q for the quarter ended June 30, 2014, filed with the SEC on August 1, 2014, and our Quarterly Report on Form 10-Q for the quarter ended September 30, 2014, filed with the SEC on November 3, 2014;

•

our Current Reports on Form 8-K filed with the SEC on February 26, 2014, March 18, 2014, April 3, 2014, and May 13, 2014; and

•

You may request a copy of these filings, at no cost, by telephoning our Investor Relations department at (617) 225-2500 or writing us at:

Investor Relations
Dyax Corp.
55 Network Drive
Burlington, Massachusetts 01803

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7,000,000 Shares

[GRAPHIC MISSING]

Common Stock

PROSPECTUS SUPPLEMENT

BofA Merrill Lynch

Cowen and Company

RBC Capital Markets

Needham & Company

Wedbush PacGrow

, 2015

PROSPECTUS SUPPLEMENT (To Prospectus Dated November 14, 2014)

7,000,000 Shares

Dyax Corp.

Common Stock

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Prospectus

ABOUT THIS PROSPECTUS SUPPLEMENT

PROSPECTUS SUPPLEMENT SUMMARY

Dyax Corp.

Recent Developments

Preliminary financial information

Our History

THE OFFERING

RISK FACTORS

Risks Related to this Offering and Our Common Stock

We have broad discretion in the use of the net proceeds from this offering and our existing cash and may not use them effectively.

If you purchase our common stock in this offering, you will incur immediate and substantial dilution in the book value of your shares.

If we sell shares of our common stock in future financings, stockholders may experience immediate dilution and, as a result, our stock price may decline.

FORWARD-LOOKING STATEMENTS

USE OF PROCEEDS

DIVIDEND POLICY

CAPITALIZATION

DILUTION

UNDERWRITING

Commissions and Discounts

Option to Purchase Additional Shares

No Sales of Similar Securities

Nasdaq Global Market Listing

Price Stabilization, Short Positions

Passive Market Making

Electronic Distribution

Other Relationships

Notice to Prospective Investors in the European Economic Area

Notice to Prospective Investors in the United Kingdom

Notice to Prospective Investors in Switzerland

Notice to Prospective Investors in the Dubai International Financial Centre

Notice to Prospective Investors in Australia

Notice to Prospective Investors in Hong Kong

Notice to Prospective Investors in Japan

Notice to Prospective Investors in Singapore

LEGAL MATTERS

EXPERTS

WHERE YOU CAN FIND MORE INFORMATION

INCORPORATION OF CERTAIN INFORMATION BY REFERENCE

Common stock Preferred stock Warrants Debt Securities Units

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ABOUT THIS PROSPECTUS

DYAX CORP.

Dyax Corp.

Our History

RISK FACTORS

FORWARD-LOOKING STATEMENTS

USE OF PROCEEDS

RATIO OF EARNINGS TO FIXED CHARGES AND RATIO OF COMBINED FIXED CHARGES AND PREFERRED STOCK DIVIDENDS TO EARNINGS

DESCRIPTION OF CAPITAL STOCK

Common Stock

Preferred Stock

Registration Rights

Dividend Policy

Delaware Anti-Takeover Law

Charter and By-law Provisions

Transfer Agent and Registrar

DESCRIPTION OF DEBT SECURITIES

General

Exchange and/or Conversion Rights

Transfer and Exchange

Certificated Debt Securities

Global Debt Securities and Book-Entry System

No Protection in the Event of Change of Control

Covenants

Consolidation, Merger and Sale of Assets

Events of Default

Modification and Waiver

Defeasance and Discharge of Debt Securities and Certain Covenants in Certain Circumstances

Regarding the Trustee

DESCRIPTION OF WARRANTS

General

Debt Warrants

Other Warrants

Exercise of Warrants

PROSPECTUS SUPPLEMENT
(To Prospectus Dated November 14, 2014)

Common stock
Preferred stock
Warrants
Debt Securities
Units

BofA Merrill Lynch

Cowen and Company

RBC Capital Markets

Needham & Company

Wedbush PacGrow