SecProbe.io

Mail Stop 4720

November 2 5, 2015

VIA E -mail
John M. Maraganore, Ph. D.
Chief Executive Officer
Alnylam Pharmaceuticals, Inc.
300 Third Street ,
Cambridge, MA  02142

Re: Alnylam  Pharmaceuticals, Inc.
 Form 10-K for Fiscal Year Ended December 31, 2014
Filed February 13 , 2015
File No. 001-36407

Dear Dr. Maraganore :

We have limited our review of your filing to the financial statements and related
disclosures and have the following comment .  In our comment, we ask you to provide us with
information so we may better understand your disclosure.

Please respond to this comment within 10 business days by providing the requ ested
information or advise  us as soon as possible  when you will respond .  If you do not believe that
our comment applies to your facts and circumstances, please tell us why in your response.

After reviewing  your response to this comment , we may have additional comments .

Notes to  Consolidate d Financial Sta tements
3. Significant Agreements, page 114

1. In order to help us understand more fully how your collaborative arrangements impact
your financial statements for each period presented, please provide us, in table format, the
amounts  by year and by line ite m included in your statements of operations attributable
to transactions arising from collaborative arrangements between you and the other
participants and third -parties.   Please provide separate tables for each of your significant
collaborative arrangeme nts and for all of your collaborative arrangements in the
aggregate (i.e. the significant arrangements and all other arrangements).  Present
separately amounts with other participants and third -parties that are netted in a financial
statement line item.  R efer to ASC 808.

Dr. John M. Maraganore, Ph.D.
Alnylam Pharmaceuticals, Inc.
November 2 5, 2015
Page 2

 We urge all persons who are responsible for the accuracy and adequacy of the disclosure
in the filing  to be certain that the filing include s the information the Securities Exchange Act of
1934 and all applicable Exchange Act rules requir e.  Since the company and its management are
in possession of all facts relating to a company’s disclosure, they are responsible for the accuracy
and adequacy of the disclosures they have made.

 In responding to our comment, please provide a written statement from the company
acknowledging that:
 the company is responsible for the adequacy and accuracy of the disclosure in the filing;
 staff comment or changes to disclosure in response to staff comment do not foreclose the
Commission from taking any act ion with respect to the filing; and
 the company may not assert staff comment as a defense in any proceeding initiated by the
Commission or any person under the federal securities laws of the United States.

You may contact Bonnie Baynes, Staff Accountant, at (202) 551 -4924  or Mary Mast,
Senior Staff Accountant, at (202) 551 -3613  if you have questions regarding this comment.  In
this regard, do not hesitate to contact me at (202) 551 -3679.

Sincerely,

 /s/ Jim B. Rosenberg

Jim B. Rosenberg
Senior Assistant Chief  Accountant
Office of Healthcare and Insurance