Consolidated Subsidiaries	12 Months Ended
Dec. 31, 2012
Consolidated Subsidiaries
Consolidated Subsidiaries	8. Consolidated Subsidiaries Hermes BioSciences, Inc. On October 6, 2009, (the "Acquisition Date"), the Company completed the acquisition of all outstanding shares of Hermes, a privately-held biotechnology company developing lipidic nano-carriers to allow for targeted delivery of small molecule drugs, including chemotherapies, with the goal of improving cancer treatment safety and efficacy. As consideration for the acquisition, the Company issued 4,383,000 shares of common stock with an estimated fair value of $9,292,000 based on an internal valuation prepared by the Company. The acquisition also included a contingent consideration arrangement that required additional shares to be issued by the Company to Hermes' former stockholders based on the occurrence and timing of certain potential future financing events. The range of additional shares that the Company could have been required to issue on the Acquisition Date as contingent consideration was between 0 and 1,100,000 and issuance could have occurred up to 24 months after the Acquisition Date. The estimated fair value of the contingent consideration recognized on the Acquisition Date of $178,000 was determined by performing a probability weighted analysis of the likelihood of occurrence of potential future financing events. That estimate was based on significant inputs not observable in the market, or Level 3 inputs. Key assumptions included management's estimates of the probabilities of such potential future financing events occurring. As of December 31, 2010, 400,000 additional shares could have been issued as contingent consideration. However, the Company determined a zero probability that the contingent consideration would ultimately be paid and recognized a gain of $178,000 for the year ended December 31, 2010. On July 8, 2011, the Company satisfied the contingent consideration triggering event, which reduced the shares that could be issued from 400,000 to zero. Silver Creek Pharmaceuticals, Inc. Silver Creek was incorporated on June 22, 2010 and commenced operations on August 20, 2010. On August 20, 2010, the Company purchased 12,000,000 shares of Silver Creek Series A preferred stock in exchange for technology licenses. On August 20, 2010 and December 17, 2010, Silver Creek issued a total of 4,190,000 shares of Silver Creek Series A preferred stock to other investors in exchange for $4,165,000, net of $25,000 of issuance costs. The Company consolidated Silver Creek on August 20, 2010, as the Company concluded that Silver Creek is a variable interest entity and the Company is the primary beneficiary. The Company has the ability to direct the activities of Silver Creek through its ownership percentage and through the board of director seats controlled by the Company and its related parties and de facto agents. As of December 31, 2011 and 2012, the Company owned 74% of the voting stock of Silver Creek and, as of December 31, 2011 and 2012, the Company recorded a non-controlling interest of $574,000 and $97,000, respectively, as a component of mezzanine equity on the Company's consolidated balance sheets based on the terms of the Silver Creek Series A preferred stock. As of December 31, 2011, the Company consolidated Silver Creek total assets and total liabilities of $2,302,000 and $39,000, respectively. As of December 31, 2012, the Company consolidated Silver Creek total assets and total liabilities of $2,202,000 and $1,763,000, respectively. As of December 31, 2011 and 2012, employees and directors of the Company owned approximately 6% of Silver Creek Series A preferred stock. Merrimack Pharmaceuticals (Bermuda) Ltd. Merrimack Pharmaceuticals (Bermuda) Ltd. was incorporated in Bermuda during 2011, is wholly owned by the Company and holds certain intellectual property rights with respect to MM-398.

8. Consolidated Subsidiaries

Hermes BioSciences, Inc.

On October 6, 2009, (the "Acquisition Date"), the Company completed the acquisition of all outstanding shares of Hermes, a privately-held biotechnology company developing lipidic nano-carriers to allow for targeted delivery of small molecule drugs, including chemotherapies, with the goal of improving cancer treatment safety and efficacy.

As consideration for the acquisition, the Company issued 4,383,000 shares of common stock with an estimated fair value of $9,292,000 based on an internal valuation prepared by the Company. The acquisition also included a contingent consideration arrangement that required additional shares to be issued by the Company to Hermes' former stockholders based on the occurrence and timing of certain potential future financing events. The range of additional shares that the Company could have been required to issue on the Acquisition Date as contingent consideration was between 0 and 1,100,000 and issuance could have occurred up to 24 months after the Acquisition Date. The estimated fair value of the contingent consideration recognized on the Acquisition Date of $178,000 was determined by performing a probability weighted analysis of the likelihood of occurrence of potential future financing events. That estimate was based on significant inputs not observable in the market, or Level 3 inputs. Key assumptions included management's estimates of the probabilities of such potential future financing events occurring.

As of December 31, 2010, 400,000 additional shares could have been issued as contingent consideration. However, the Company determined a zero probability that the contingent consideration would ultimately be paid and recognized a gain of $178,000 for the year ended December 31, 2010. On July 8, 2011, the Company satisfied the contingent consideration triggering event, which reduced the shares that could be issued from 400,000 to zero.

Silver Creek Pharmaceuticals, Inc.

Silver Creek was incorporated on June 22, 2010 and commenced operations on August 20, 2010. On August 20, 2010, the Company purchased 12,000,000 shares of Silver Creek Series A preferred stock in exchange for technology licenses. On August 20, 2010 and December 17, 2010, Silver Creek issued a total of 4,190,000 shares of Silver Creek Series A preferred stock to other investors in exchange for $4,165,000, net of $25,000 of issuance costs. The Company consolidated Silver Creek on August 20, 2010, as the Company concluded that Silver Creek is a variable interest entity and the Company is the primary beneficiary. The Company has the ability to direct the activities of Silver Creek through its ownership percentage and through the board of director seats controlled by the Company and its related parties and de facto agents. As of December 31, 2011 and 2012, the Company owned 74% of the voting stock of Silver Creek and, as of December 31, 2011 and 2012, the Company recorded a non-controlling interest of $574,000 and $97,000, respectively, as a component of mezzanine equity on the Company's consolidated balance sheets based on the terms of the Silver Creek Series A preferred stock.

As of December 31, 2011, the Company consolidated Silver Creek total assets and total liabilities of $2,302,000 and $39,000, respectively. As of December 31, 2012, the Company consolidated Silver Creek total assets and total liabilities of $2,202,000 and $1,763,000, respectively.

As of December 31, 2011 and 2012, employees and directors of the Company owned approximately 6% of Silver Creek Series A preferred stock.

Merrimack Pharmaceuticals (Bermuda) Ltd.

Merrimack Pharmaceuticals (Bermuda) Ltd. was incorporated in Bermuda during 2011, is wholly owned by the Company and holds certain intellectual property rights with respect to MM-398.