January 3, 2018
VIA EDGAR SUBMISSION
Securities and Exchange Commission
Division of Corporation Finance
100 F Street, NE
Washington, DC 20549
Attention: Ada D. Sarmento.
| Re: | Merrimack Pharmaceuticals, Inc. |
| Registration Statement on FormS-3 |
| FileNo. 333-222093 |
| Request for Acceleration |
Ladies and Gentlemen:
Pursuant to Rule 461 under the Securities Act of 1933, as amended, Merrimack Pharmaceuticals, Inc. hereby requests acceleration of the effective date of its Registration Statement on FormS-3 (FileNo. 333-222093), so that it may become effective at 4:30 p.m., Eastern time, on January 5, 2018, or as soon as practicable thereafter.
| Very truly yours, | ||
| By: | /s/ Jeffrey A. Munsie | |
Jeffrey A. Munsie General Counsel | ||
