Ownership Submission
FORM 4
Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).
UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP OF SECURITIES

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940
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(Print or Type Responses)
1. Name and Address of Reporting Person *
Kelly William J
   2. Issuer Name and Ticker or Trading Symbol
REPLIGEN CORP [RGEN] 		5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)
_____ Director _____ 10% Owner
__X__ Officer (give title below) _____ Other (specify below)
CFO
(Last)
(First)
(Middle)
C/O REPLIGEN CORPORATION, 41 SEYON STREET, BLDG 1, STE 100		 3. Date of Earliest Transaction (Month/Day/Year)
08/31/2012
(Street)

WALTHAM, MA 02453		 4. If Amendment, Date Original Filed(Month/Day/Year)
 6. Individual or Joint/Group Filing(Check Applicable Line)
_X_ Form filed by One Reporting Person
___ Form filed by More than One Reporting Person
(City)
(State)
(Zip)
Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1.Title of Security
(Instr. 3)		 2. Transaction Date (Month/Day/Year) 2A. Deemed Execution Date, if any (Month/Day/Year) 3. Transaction Code
(Instr. 8)		 4. Securities Acquired (A) or Disposed of (D)
(Instr. 3, 4 and 5)		 5. Amount of Securities Beneficially Owned Following Reported Transaction(s)
(Instr. 3 and 4)		 6. Ownership Form: Direct (D) or Indirect (I)
(Instr. 4)		 7. Nature of Indirect Beneficial Ownership
(Instr. 4)
Code V Amount (A) or (D) Price
Common Stock 08/31/2012   M   80,000 A $ 4.82 85,000 D  
Common Stock 08/31/2012   M   10,000 A $ 3.33 95,000 D  
Common Stock 08/31/2012   S   40,409 D $ 5.5 54,591 D  
Common Stock 08/31/2012   S   8,500 D $ 5.51 46,091 D  
Common Stock 08/31/2012   S   10,700 D $ 5.52 35,391 D  
Common Stock 08/31/2012   S   9,681 D $ 5.53 25,710 D  
Common Stock 08/31/2012   S   8,000 D $ 5.54 17,710 D  
Common Stock 08/31/2012   S   9,900 D $ 5.55 7,810 D  
Common Stock 08/31/2012   S   4,803 D $ 5.56 3,007 D  
Common Stock 08/31/2012   S   800 D $ 5.57 2,207 D  
Common Stock 08/31/2012   S   1,500 D $ 5.59 707 D  
Common Stock 08/31/2012   S   400 D $ 5.6 307 D  
Common Stock 08/31/2012   S   100 D $ 5.61 207 D  
Common Stock 08/31/2012   S   107 D $ 5.62 100 D  
Common Stock 08/31/2012   S   100 D $ 5.63 0 D  

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Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned
(e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security
(Instr. 3)		 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (Month/Day/Year) 3A. Deemed Execution Date, if any (Month/Day/Year) 4. Transaction Code
(Instr. 8)		 5. Number of Derivative Securities Acquired (A) or Disposed of (D)
(Instr. 3, 4, and 5)		 6. Date Exercisable and Expiration Date
(Month/Day/Year)		 7. Title and Amount of Underlying Securities
(Instr. 3 and 4)		 8. Price of Derivative Security
(Instr. 5)		 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s)
(Instr. 4)		 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I)
(Instr. 4)		 11. Nature of Indirect Beneficial Ownership
(Instr. 4)
Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares
Stock Option (Right to Buy) $ 4.82 08/31/2012   M     80,000   (1) 03/31/2018 Common Stock 80,000 $ 0 45,000 D  
Stock Option (Right to Buy) $ 3.33 08/31/2012   M     10,000   (2) 07/15/2020 Common Stock 10,000 $ 0 35,000 D  

Reporting Owners

Reporting Owner Name / Address Relationships
 Director  10% Owner  Officer  Other
Kelly William J
C/O REPLIGEN CORPORATION
41 SEYON STREET, BLDG 1, STE 100
WALTHAM, MA 02453		       CFO  

Signatures

 William J. Kelly (Attorney in Fact)   09/04/2012
**Signature of Reporting Person Date

Explanation of Responses:

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
(1) 20,000 shares vested and became exercisable at each of the following dates: 3/31/2009, 3/31/2010, 3/31/2011 and 3/31/2012.
(2) 5,000 shares each vested and became exercisable at 7/15/2011 and 7/15/2012.

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