Maxygen Announces Tax Treatment of 2012 Cash Distribution

Maxygen, Inc. (Nasdaq: MAXY), a biotechnology company, today announced that its distribution of cash in September 2012 primarily will be classified as a return of capital to its stockholders for U.S. Federal income tax purposes.

On September 6, 2012, Maxygen distributed approximately $100.0 million in cash to its stockholders. The table below summarizes the U.S. Federal income tax treatment of the distribution for the common stock of Maxygen:

Maxygen’s tax return for the year ended December 31, 2012 has not been filed. As a result, the tax treatment for the distribution discussed above has been calculated using the best available information as of the date of this release.

The information in this document represents Maxygen’s understanding of existing U.S. Federal income tax laws and regulations and does not address state, local or international tax consequences. Please note that federal tax laws affect taxpayers differently, and the information in this release is not intended as tax or investment advice or advice to stockholders on how the distribution should be reported on their tax returns. Maxygen’s stockholders are urged to consult with their own tax advisors regarding the specific tax consequences to them of receipt of the cash distribution, including but not limited to, the application to them of Federal estate and gift, state, local, foreign and other tax laws.

About Maxygen

Maxygen is a biotechnology company that has historically focused on the discovery and development of improved next-generation protein pharmaceuticals for the treatment of disease and serious medical conditions. Maxygen continues to retain all rights to its MAXY-G34 product candidate, a next-generation pegylated, granulocyte colony stimulating factor, or G-CSF, for the treatment of chemotherapy-induced neutropenia and acute radiation syndrome. For more information, please visit our website at www.maxygen.com.