X0306 4 2013-05-09 0 0000730272 REPLIGEN CORP RGEN 0001241821 GRIFFITH MICHAEL A C/O REPLIGEN CORPORATION 41 SEYON ST, BLDG 1, STE 100 WALTHAM MA 02453 1 0 0 0 Common Stock 2013-05-09 4 A 0 5342 0 A 7342 D Mr. Griffith was awarded 5,342 Restricted Stock Units. Each Restricted Stock Unit represents a contingent right to receive one share of Repligen Corporation's Common Stock. The Restricted Stock Units vest on May 9, 2014. The Restricted Stock Units may be settled only by delivering shares of Repligen Corporation's Common Stock, and thus, the grant is being reported in Table 1 as allowed per SEC guidance. /s/ William J. Kelly (Attorney in Fact) 2013-05-16