REPLIGEN CORP — Director's Dealing 2009

May 20, 2009

SEC Form 3 — Initial Statement of Beneficial Ownership

Issuer: REPLIGEN CORP (RGEN)
CIK: 0000730272
Period of Report: 2009-05-15

Reporting Person: BVF PARTNERS L P/IL (10% Owner, Group Member)
Reporting Person: BIOTECHNOLOGY VALUE FUND L P (10% Owner, Group Member)
Reporting Person: BIOTECHNOLOGY VALUE FUND II LP (10% Owner, Group Member)
Reporting Person: BVF INVESTMENTS LLC (10% Owner, Group Member)
Reporting Person: BVF INC/IL (10% Owner, Group Member)
Reporting Person: LAMPERT MARK N (10% Owner, Group Member)

Holdings (Non-Derivative)

Security	Shares	Ownership
Common Stock	825750	Direct
Common Stock	534400	Direct
Common Stock	1856700	Direct
Common Stock	3216850	Indirect
Common Stock	3216850	Indirect
Common Stock	3216850	Indirect

Footnotes

F1: The shares of Common Stock are directly beneficially owned by Biotechnology Value Fund, L.P. ("BVF"), a Delaware limited
partnership.

F2: The shares of Common Stock are directly beneficially owned by Biotechnology Value Fund II, L.P. ("BVF2"), a Delaware limited
partnership.

F3: The shares of Common Stock are directly beneficially owned by BVF Investments, LLC ("BVFLLC"), a Delaware limited liability
company. Pursuant to the operating agreement of BVFLLC, BVF Partners, L.P., a Delaware limited partnership ("Partners") is
authorized, among other things, to invest the contributed capital of Samana Capital, L.P., the majority member of BVFLLC, in
the shares of Common Stock and other securities and to vote, exercise or convert and dispose of such securities and is
entitled to receive fees based on assets under management and, subject to certain exceptions, allocations based on realized
and unrealized gains on such assets.

F4: The shares of Common Stock are indirectly beneficially owned by Partners. Partners is the general partner of BVF and BVF2
and is the manager of BVFLLC.

F5: The shares of Common Stock are indirectly beneficially owned by BVF Inc., a Delaware corporation ("BVF Inc."). BVF Inc. is
the general partner of Partners.

F6: Mark N. Lampert is the sole shareholder, sole director, and an officer of BVF Inc.