SecProbe.io

December 2, 2013

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 the fiscal year ended December 31, 2012
Filed February 19, 2013
File No. 000-50743

Dear Dr. Maraganore :

We have reviewed your filing an d have the following comments.  In some of our
comments, we may ask you to provide us with information so  we may better understand your
disclosure.

Please respond to this letter within ten business days by amending your filing, by
providing the requested information, or by advising us when you will provide the requested
response.   If you do not believe our c omments apply to your facts and circumstances or do not
believe an amendment is appropriate, please tell us why in your response.

After reviewing any amendment to your filing and the information you provide in
response to these  comments, we may have  additional comments.

ALN -VSP — Liver Cancer, page 13

1. We note the disclosure on page 14 indicating tha t you have a license agreement with
Ascletis . Please disclose the material terms of this agreement under a separate caption,
including the patents licensed under this agreement and how they apply to your products,
all other material rights and obligations of both parties, the duration, material termination
provisions, payment provisions  and prior and potential future payments. Additionally,
please file this agreement as an exhibit pursuant to Item 601(b)(10) of Regulation S -K.
Alternatively, please provide us with an analysis supporting your determination that you
are not substantially dependent upon this agreement.

Medtronic, page 19

2. We no te that you entered into a collaboration agreement with Medtronic.  Please  disclose
the milestone payments paid to date  and aggregate potential milestone payments that may

John M. Maraganore, Ph.D.
Alnylam Pharmaceuticals, Inc.
December 2, 2013
Page 2

 be paid in the future. Please  revise your disclosure to provide information about the
royalty rate. For example, you may either provide a range of royalties within ten percent
or a statement that the percentage is in the teens, twenties, etc.  Additionally, p lease
provide more precise information about the royalty term by stating the years during
which the relevant patents will expire in each relevant jurisdiction.

The Medicines Company, page 22

3. We note that you entered into a license agreement with MedCo.  Please  revise your
disclosure to provide more precise information about the royalty  rate. For example, you
may either provide a range of royalties within ten percent or a statement that the
percentage is in the teens, twenties, etc.  Additionally, please file this agreement as an
exhibit pursuant to Item 601(b)(10) of Regulation S -K. Alte rnatively, please provide us
with an analysis supporting your determination that you are not substantially dependent
upon this agreement .

Arrowhead, page 24

4. We note that you have a collaboration  agreement with Arrowhead . Please disclose the
material ter ms of this agreement under a separate caption, including the patents licensed
under this agreement and how they apply to your products, all other material rights and
obligations of both parties, the duration, material termination provisions, and payment
terms and the prior and potential future payments. Additionally, please file this agreement
as an exhibit pursuant to Item 601(b)(10) of Regulation S -K. Alternatively, please
provide us with an analysis supporting your determination that you are not substantially
dependent upon this agreement .

Tekmira, page 24

5. We note your reference in the third full paragraph on page 25 to a significant buy down
of milestone payments and a reduction of royalty rates payable to Tekmira resulting from
the 2012 cross -licensing agreement. Please provide a range for the reduced roya lty rate
within ten percent.

We urge all persons who are responsible for the accuracy and adequacy of the disclosure
in the filing to be certain that the filing includes the information the Securities Exchange Act of
1934 and all applicable Exchange Act rules require.   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 comments, 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;

John M. Maraganore, Ph.D.
Alnylam Pharmaceuticals, Inc.
December 2, 2013
Page 3

 staff comments or changes to disclosure in response to staff comments do not foreclose
the Commission from taking any action with respect to the filing; and

 the company may not assert staff comments as a defense in any proceeding initiated by
the Commission or any person under the federal securities laws of the United States.

Please contact Matthew Jones  at (202) 551 -3786 or me at (202) 551 -3715 with any other
questions.

Sincerely,

 /s/ Jeffrey P. Riedler

Jeffrey P. Riedler
Assistant Director