REPLIGEN CORP — Director's Dealing 2011

Mar 31, 2011

SEC Form 4 — Statement of Changes in Beneficial Ownership

Issuer: REPLIGEN CORP (RGEN)
CIK: 0000730272
Period of Report: 2011-03-30

Reporting Person: WITT DANIEL P (Vice President)

Derivative Transactions

Date	Security	Exercise Price	Code	Shares	A/D	Expiration	Underlying	Ownership
2011-03-30	Stock Option (Right to Buy)	$2.66	D	10000	Disposed	2011-04-03	Common Stock (10000)	Direct

Footnotes

F1: The option was cancelled by mutual agreement of the Rporting Person and the Issuer in advance of its scheduled expiration date. The Reporting Person received the difference between $3.70, the closing price of the ISsuer's Common Stock on the transaction date, and $2.66, the exercise price of the stock option, less any applicable withholding taxes.