EXHIBIT 5.1

                          Morgan, Lewis & Bockius LLP
                              1701 Market Street
                            Philadelphia, PA 19103



November 20, 2001




Genaera Corporation
5110 Campus Drive
Plymouth Meeting, PA 19462

Ladies and Gentlemen:

We have acted as counsel for Genaera Corporation, a Delaware corporation (the
"Company"), in connection with the Registration Statement on Form S-3 (the
"Registration Statement") under the Securities Act of 1933, as amended (the
"Act"), relating to the proposed offer and sale by the Company from time to
time, as set forth in the prospectus contained in the Registration Statement
(the "Prospectus") and as shall be set forth in one or more supplements to the
Prospectus (each, a "Prospectus Supplement") of up to $50,000,000 aggregate
offering price of securities (the "Securities") which may include any or all of
(i) shares of Common Stock, par value $.002 per share, of the Company (the
"Common Stock"), (ii) shares of Preferred Stock, par value $.01 per share, of
the Company (the "Preferred Stock") and (iii) warrants to purchase Common Stock
or Preferred Stock (the "Warrants").

In connection with this opinion, we have examined a copy of (a) the Registration
Statement; (2) the Company's Restated Certificate of Incorporation, as amended
(the "Certificate"); (3) the Company's Amended and Restated By-laws (the
"By-laws"); (4) certain resolutions of the Company's Board of Directors relating
to the Registration Statement, and (5) such other documents as we have deemed
appropriate. In our examination, we have assumed the genuineness of all
signatures, the authenticity of all documents submitted to us as originals, and
the conformity to authentic original documents of all documents submitted to us
as copies. With respect to matters of fact relevant to our opinion, we have
relied upon certificates of officers of the Company, representations made by the
Company in other documents examined by us and other representations of officers
of the Company. We have also obtained and relied upon such certificates and
assurances from public officials as we have deemed necessary.

For the purpose of the opinions set forth below, we have assumed, without
independent investigation, that (1) the issuance, sale, number and terms of
Securities to be offered from time to time will be duly authorized and
established, in accordance with the Certificate, the By-laws and applicable
Delaware law (each, a "Board Action"); (2) prior to any issuance of shares of a
series of Preferred Stock, an appropriate Certificate of Designation relating to
such series of Preferred Stock will have been duly authorized by Board Action
and filed with the Secretary of State of Delaware; (3) any Warrants will be
issued under one or more warrant agreements (each, a "Warrant Agreement")
between the Company and financial institution identified in the Warrant
Agreement as a warrant agent (each, a "Warrant Agent"); (4) the Registration
Statement and any amendments thereto (including post-effective amendments) will
have become effective and comply with all applicable laws; (5) the Registration
Statement will be effective and will comply with all applicable laws at the time
the Securities are offered or issued as contemplated by the Registration
Statement; (6) a Prospectus Supplement or term sheet will have been prepared and
filed with the Securities and Exchange Commission describing the Securities
offered thereby and will comply with all applicable laws; (7) all Securities
will be issued and sold in compliance with applicable federal and state
securities laws; and (8) a definitive purchase, underwriting or similar
agreement with respect to any Securities offered or issued will have been duly
authorized and validly executed and delivered by the Company and the other
parties thereto.


Subject to the foregoing and the other matters set forth herein, it is our
opinion that, as of the date hereof:

1.   Upon due authorization by Board Action of the issuance and sale of shares
of the Common Stock and upon issuance and delivery of such shares of Common
Stock against payment for such shares (in an amount at least equal to the par
value of the Common Stock) in accordance with the terms of the Board Action and
as contemplated by the Registration Statement and/or the applicable Prospectus
Supplement, and, if applicable, upon the exercise of any Warrants or conversion
of any Preferred Stock in accordance with their respective terms (which shall,
in either case, provide for payment of consideration that shall be at least
equal to the par value of Common Stock), such shares of Common Stock will be
validly issued, fully paid and nonassessable.

2.   Upon due authorization by Board Action of the issuance and sale of shares
of a series of Preferred Stock and upon issuance and delivery of such shares of
Preferred Stock against payment for such shares (in an amount at least equal to
the par value of the Preferred Stock) in accordance with the terms of the Board
Action and as contemplated by the Registration Statement and/or the applicable
Prospectus Supplement, and, if applicable, upon the exercise of any Warrants in
accordance with its terms (which shall provide for payment of consideration at
least equal to the par value of the Preferred Stock), such shares of such series
of Preferred Stock will be validly issued, fully paid and nonassessable.

3.   When a Warrant Agreement providing for the specific terms of a particular
issuance of Warrants has been duly authorized by Board Action and has been duly
executed and delivered by the Company and the Warrant Agent named in the Warrant
Agreement, and Warrants conforming to the requirements of the related Warrant
Agreement have been duly countersigned or authenticated, as required, by the
Warrant Agent and duly executed and delivered by the Company against payment for
such Warrants in accordance with the terms of the Warrant Agreement and as
contemplated by the Registration Statement and/or the applicable Prospectus
Supplement, such Warrants will constitute valid and binding obligations of the
Company.

To the extent that the obligations of the Company under each Warrant Agreement
may be dependent upon such matters, we assume for purposes of this opinion that
the Warrant Agent is duly organized, validly existing and in good standing under
the laws of its jurisdiction of organization; that the Warrant Agent is duly
qualified to engage in the activities contemplated by the Warrant Agreement;
that the Warrant Agreement has been duly authorized, executed and delivered by
the Warrant Agent and constitutes the legal, valid and binding obligation of the
Warrant Agent, enforceable against the Warrant Agent in accordance with its
terms; that the Warrant Agent is in compliance, generally and with respect to
acting as a Warrant Agent under the Warrant Agreement, with all applicable laws
and regulations; and that the Warrant Agent has the requisite organizational and
legal power and authority to perform its obligations under the Warrant
Agreement.

The opinion set forth in clause 3 above is subject to the following exceptions,
limitations and qualifications: (i) the effect of bankruptcy, insolvency,
reorganization, fraudulent conveyance, moratorium or other similar laws now or
hereafter in effect relating to or affecting the rights or remedies of
creditors; (ii) the effect of general principles of equity, whether enforcement
is considered in a proceeding in equity or at law, and the discretion of the
court before which any proceeding therefor may be brought; and (iii) the
unenforceability under certain circumstances under law or court decisions of
provisions providing for the indemnification of or contribution to a party with
respect to a liability where such indemnification or contribution is contrary to
public policy.

The foregoing opinions are limited to the General Corporation Law of the State
of Delaware.

We consent to your filing this opinion as an exhibit to the Registration
Statement and to the reference to our firm under the caption "Legal Matters" in
the prospectus included therein. In giving such opinion, we do not hereby admit
that we are acting within the category of persons whose consent is required
under Section 7 of the Act or the rules or regulations of the Securities and
Exchange Commission thereunder.


Very truly yours,

/s/ Morgan, Lewis & Bockius LLP