This excerpt taken from the XNPT DEF 14A filed Mar 31, 2006.
Investors Rights Agreement
We have entered into an investors rights agreement with the prior holders of our preferred stock and certain warrants, including entities with which certain of our directors are affiliated. Pursuant to the agreement, these stockholders are entitled to rights with respect to the registration of their shares under the Securities Act, subject to certain limitations and restrictions. Also, if at any time we propose to register any of our securities under the Securities Act, either for our own account or for the account of other securities holders, the holders of these shares will be entitled to notice of the registration and, subject to certain exceptions, may be entitled to include, at our expense, their shares of XenoPort common stock in the registration. In addition, the holders of these shares may require us, at our expense and on not more than two occasions, to file a registration statement covering their shares of XenoPort common stock, and we will be required to use our commercially reasonable efforts to have the registration statement declared effective.