REPLIGEN CORP — Director's Dealing 2013

May 7, 2013

SEC Form 4 — Statement of Changes in Beneficial Ownership

Issuer: REPLIGEN CORP (RGEN)
CIK: 0000730272
Period of Report: 2013-05-06

Reporting Person: Benjamin Howard (VP Business Development)

Non-Derivative Transactions

Date	Security	Code	Shares	Price	A/D	Holdings After	Ownership
2013-05-06	Common Stock	M	12964	$4.25	Acquired	22964	Direct
2013-05-06	Common Stock	F	6233	$8.84	Disposed	16731	Direct
2013-05-06	Common Stock	M	10000	$3.33	Acquired	26731	Direct
2013-05-06	Common Stock	F	3767	$8.84	Disposed	22964	Direct

Derivative Transactions

Date	Security	Exercise Price	Code	Shares	A/D	Expiration	Underlying	Ownership
2013-05-06	Stock Option (Right to Buy)	$4.25	M	12964	Disposed	2019-02-11	Common Stock (12964)	Direct
2013-05-06	Stock Option (Right to Buy)	$3.33	M	10000	Disposed	2020-07-15	Common Stock (10000)	Direct

Footnotes

F1: Payment made via forfeiture of 6,233 shares of Common Stock valued at the Closing Price of $8.84 on May 6, 2013.

F2: Payment made via forfeiture of 3,767 shares of Common Stock valued at the Closing Price of $8.84 on May 6, 2013.