X0202 4 2006-08-10 0 0001060736 SEATTLE GENETICS INC /WA SGEN 0001307729 Baker Brothers Life Sciences Capital (GP), LLC 667 MADISON AVENUE 17TH FLOOR NEW YORK NY 10021 1 0 1 0 0001087939 BAKER JULIAN 667 MADISON AVENUE NEW YORK NY 10021 0 0 1 0 0001087940 BAKER FELIX 667 MADISON AVENUE NEW YORK NY 10021 1 0 1 0 Common Stock 2006-08-10 4 P 0 1038 4.0368 A 4003360 I See Footnote Common Stock 2006-08-10 4 P 0 2559 4.03 A 4005919 I See Footnote Common Stock 2006-08-11 4 P 0 106622 4.0291 A 4112541 I See Footnote In addition to Baker Brothers Life Sciences Capital (GP), LLC this form 4 is being filed jointly by Julian C. Baker, Felix J. Baker, each of whom has the same business address as Baker Brothers Life Sciences Capital (GP), LLC. and may be deemed to have a pecuniary interest in securities owned by it. Because of certain relationships with other security holders of the Issuer, the Reporting Persons have filed on Schedule 13D as if they were a member of a group with such shareholders. (Continued in footnote 2.) However, the Reporting Persons disclaim that they and any other person or persons, including those persons with whom the Reporting Persons have filed a Schedule 13D, in fact constitute a "group" for purposes of Section 13(d)(3) of the Securities Exchange Act of 1934, as amended, or Rule 13d-5 thereunder or that they are the beneficial owners of securities owned by such other persons, and each of them disclaims beneficial ownership of securities reported herein except to the extent of their pecuniary interest, if any, therein. Felix J. Baker is a director of the Issuer. Represents shares of common stock owned directly by Baker Brothers Life Sciences, LP., the sole general partner of which is Baker Brothers Life Sciences Capital, L.P., a limited partnership of which the sole general partner is Baker Brothers Life Sciences Capital (GP), LLC. Felix J. Baker and Julian C. Baker are the controlling members of Baker Brothers Life Sciences Capital (GP), LLC. /s/ Julian C. Baker, as Managing Member of Baker Brothers Life Sciences Capital (GP), LLC 2006-08-15 /s/ Julian C. Baker 2006-08-15 /s/ Felix J. Baker 2006-08-15