Joint Filing Agreement
Exhibit A
The undersigned hereby agree that the statement on Schedule 13G with respect to the Common
Stock, $0.001 par value of XenoPort, Inc., dated as of February 14, 2006, is, and any amendments
thereto (including amendments on Schedule 13D) signed by each of the undersigned shall be, filed on
behalf of each of us pursuant to and in accordance with the provisions of Rule 13d-1(k) under the
Securities Exchange Act of 1934.
Date: February 14, 2006
| MAVERICK CAPITAL, LTD. | ||||||||
| By: | Maverick Capital Management, LLC | |||||||
| Its General Partner | ||||||||
| By: | ▇▇▇ ▇. ▇▇▇▇▇▇▇ III, Manager | |||||||
| By: | /s/ ▇▇▇▇ ▇. ▇▇▇▇▇▇▇▇▇▇ | |||||||
| ▇▇▇▇ ▇. ▇▇▇▇▇▇▇▇▇▇ | ||||||||
| Under Power of Attorney dated | ||||||||
| February 13, 2003 | ||||||||
| MAVERICK CAPITAL MANAGEMENT, LLC | ||||||||
| By: | ▇▇▇ ▇. ▇▇▇▇▇▇▇ III, Manager | |||||||
| By: | /s/ ▇▇▇▇ ▇. ▇▇▇▇▇▇▇▇▇▇ | |||||||
| ▇▇▇▇ ▇. ▇▇▇▇▇▇▇▇▇▇ | ||||||||
| Under Power of Attorney dated | ||||||||
| February 13, ▇▇▇▇ | ||||||||
| ▇▇▇ ▇. ▇▇▇▇▇▇▇ III | ||||||||
| By: | /s/ ▇▇▇▇ ▇. ▇▇▇▇▇▇▇▇▇▇ | |||||||
| ▇▇▇▇ ▇. ▇▇▇▇▇▇▇▇▇▇ | ||||||||
| Under Power of Attorney dated | ||||||||
| February 13, 2003 | ||||||||