Ownership Submission
FORM 3
 UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

INITIAL STATEMENT OF 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 *
  Tong Jeffrey K
 2. Date of Event Requiring Statement (Month/Day/Year)
01/01/2010		 3. Issuer Name and Ticker or Trading Symbol
INFINITY PHARMACEUTICALS, INC. [INFI]
(Last)
(First)
(Middle)
C/O INFINITY PHARMACEUTICALS, INC., 780 MEMORIAL DRIVE		 4. Relationship of Reporting Person(s) to Issuer
(Check all applicable)
_____ Director _____ 10% Owner
__X__ Officer (give title below) _____ Other (specify below)
VP, Cor. & Product Development
 5. If Amendment, Date Original Filed(Month/Day/Year)
(Street)

CAMBRIDGE, MA 02139		 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 Beneficially Owned
1.Title of Security
(Instr. 4)		 2. Amount of Securities Beneficially Owned
(Instr. 4)		 3. Ownership Form: Direct (D) or Indirect (I)
(Instr. 5)		 4. Nature of Indirect Beneficial Ownership
(Instr. 5)
Common Stock 17,246
D
 

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly. SEC 1473 (7-02)
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Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security
(Instr. 4)		 2. Date Exercisable and Expiration Date
(Month/Day/Year)		 3. Title and Amount of Securities Underlying Derivative Security
(Instr. 4)		 4. Conversion or Exercise Price of Derivative Security 5. Ownership Form of Derivative Security: Direct (D) or Indirect (I)
(Instr. 5)		 6. Nature of Indirect Beneficial Ownership
(Instr. 5)
Date Exercisable Expiration Date Title Amount or Number of Shares
Stock Option (Right to Buy) 05/05/2003(1) 05/05/2013 Common Stock 1,203 $ 1.72 D  
Stock Option (Right to Buy) 05/10/2005(2) 05/10/2015 Common Stock 54,672 $ 2.04 D  
Stock Option (Right to Buy) 03/31/2006(1) 03/31/2016 Common Stock 5,856 $ 3.48 D  
Stock Option (Right to Buy)   (3) 01/25/2017 Common Stock 42,418 $ 13.59 D  
Stock Option (Right to Buy)   (4) 12/13/2017 Common Stock 20,815 $ 9.8 D  
Stock Option (Right to Buy)   (5) 12/04/2018 Common Stock 35,415 $ 7.18 D  

Reporting Owners

Reporting Owner Name / Address Relationships
Director 10% Owner Officer Other
Tong Jeffrey K
C/O INFINITY PHARMACEUTICALS, INC.
780 MEMORIAL DRIVE
CAMBRIDGE, MA 02139		       VP, Cor. & Product Development  

Signatures

/s/ Jeffrey K Tong 01/07/2010
**Signature of Reporting Person Date

Explanation of Responses:

* If the form is filed by more than one reporting person, see Instruction 5(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) This stock option was granted under the issuer's Pre-Merger Stock Incentive Plan, which permits the early exercise of unvested stock options in exchange for shares of restricted stock that are subject to a right of repurchase by the issuer that lapses in accordance with the vesting schedule of the original option. This option is fully vested.
(2) This option was granted under the issuer's Pre-Merger Stock Incentive Plan, which permits the early exercise of unvested stock options in exchange for shares of restricted stock that are subject to a right of repurchase by the issuer that lapses in accordance with the vesting schedule of the original option. This option is currently vested as to 46,718 shares and vests as to the remaining shares in equal monthly installments through December 31, 2010.
(3) The option vests as to 1/48th of the shares on January 31, 2007 and vests as to 1/48th of the shares at the end of each calendar month thereafter.
(4) The option vests as to 1/48th of the shares on December 31, 2007 and vests as to 1/48th of the shares at the end of each calendar month thereafter.
(5) The option vests as to 1/48th of the shares on December 31, 2008 and vests as to 1/48th of the shares at the end of each calendar month thereafter.

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