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UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G

Under the Securities Exchange Act of 1934

SEATTLE GENETICS, INC.
(Name of Issuer)
Common Stock, $.001 par value per share
(Title of Class of Securities)
	812578102
(CUSIP Number)
March 7, 2001
(Date of Event Which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

    / /      Rule 13d-1(b)

    /x/      Rule 13d-1(c)

    / /      Rule 13d-1(d)

    *The remainder of this cover page shall be filled out for a reporting person's initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter the disclosures provided in a prior cover page.

    The information required in the remainder of this cover page shall not be deemed to be "filed" for the purpose of Section 18 of the Securities Exchange Act of 1934 ("Act") or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

CUSIP No.      812578102    

(1)	NAMES OF REPORTING PERSONS
	Cascade Investment, L.L.C.
	S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSONS
(2)	CHECK THE APPROPRIATE BOX IF A	(a)	/ /
	MEMBER OF A GROUP	(b)	/ /
(3)	SEC USE ONLY
(4)	CITIZENSHIP OR PLACE OF ORGANIZATION
	State of Washington
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH:		(5)	SOLE VOTING POWER
			-0-
		(6)	SHARED VOTING POWER
			3,521,088
		(7)	SOLE DISPOSITIVE POWER
			- -0-
		(8)	SHARED DISPOSITIVE POWER
			3,521,088
(9)	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
	3,521,088
(10)	CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES  / /
(11)	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)
	12.04%
(12)	TYPE OF REPORTING PERSON
	CO

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(1)	NAMES OF REPORTING PERSONS
	William H. Gates III
	S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSONS
(2)	CHECK THE APPROPRIATE BOX IF A	(a)	/ /
	MEMBER OF A GROUP	(b)	/ /
(3)	SEC USE ONLY
(4)	CITIZENSHIP OR PLACE OF ORGANIZATION
	United States of America
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH:		(5)	SOLE VOTING POWER
			-0-
		(6)	SHARED VOTING POWER
			3,521,088
		(7)	SOLE DISPOSITIVE POWER
			- -0-
		(8)	SHARED DISPOSITIVE POWER
			3,521,088
(9)	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
	3,521,088
(10)	CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES  / /
(11)	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)
	12.04%
(12)	TYPE OF REPORTING PERSON
	IN

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Item 1.
	(a)	Name of Issuer: Seattle Genetics, Inc. (the "Issuer")
	(b)	Address of Principal Executive Offices of the Issuer: 22215 26th Ave., SE, Suite 3000, Bothell, WA 98021
Item 2.
	(a)	Name of Persons Filing:
		(1)	Cascade Investment, L.L.C. ("Cascade")
		(2)	William H. Gates III
	(b)	Address of Principal Business Office:
		(1)	2365 Carillon Point, Kirkland, Washington 98033
		(2)	One Microsoft Way, Redmond, Washington 98052
	(c)	Citizenship:
		(1)	Cascade is a limited liability company organized under the laws of the State of Washington
		(2)	William H. Gates III is a citizen of the United States of America
	(d)	Title of Class of Securities: Common Stock, $.001 par value per share
	(e)	CUSIP Number: 812578102
Item 3.	Not Applicable
Item 4.	Ownership.
	(a)	Amount beneficially owned: 3,521,088
	(b)	Percent of class: 12.04%
	(c)	Number of shares as to which the person has:
		(i)	Sole power to vote or to direct the vote -0-
		(ii)	Shared power to vote or to direct the vote 3,521,088*
		(iii)	Sole power to dispose or to direct the disposition of -0-
		(iv)	Shared power to dispose or to direct the disposition of 3,521,088*
			* All shares held by Cascade may be deemed to be beneficially owned by William H. Gates III as the sole member of Cascade.
Item 5.	Ownership of Five Percent or Less of a Class: Not Applicable
Item 6.	Ownership of More than Five Percent on Behalf of Another Person: Not Applicable
Item 7.	Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on By the Parent Holding Company: Not Applicable
Item 8.	Identification and Classification of Members of the Group: Not Applicable
Item 9.	Notice of Dissolution of a Group: Not Applicable
Item 10.	Certification:
	By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect.

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SIGNATURE

    After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

March 19, 2001 Date
CASCADE INVESTMENT, L.L.C.
By:	/s/ MICHAEL LARSON Michael Larson, Manager
WILLIAM H. GATES III
/s/ MICHAEL LARSON William H. Gates III, by Michael Larson as attorney in fact*

JOINT FILING AGREEMENT

    We, the signatories of the statement to which this Joint Filing Agreement is attached, hereby agree that such statement is filed, and any amendments thereto filed by either or both of us will be filed, on behalf of each of us.

DATED: March 19, 2001
	CASCADE INVESTMENT, L.L.C.
	By:	/s/ MICHAEL LARSON Michael Larson, Manager
	WILLIAM H. GATES III
	/s/ MICHAEL LARSON William H. Gates III, by Michael Larson as attorney in fact*

    * Duly authorized under power of attorney dated March 14, 2001, by and on behalf of William H. Gates III, filed with Cascade's Amendment No. 1 to Schedule 13D with respect to Pan American Silver Corp. on March 19, 2001, SEC File No. 005-52919, and incorporated by reference herein.

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SIGNATURE
JOINT FILING AGREEMENT