EXHIBIT 23.1 CONSENT OF ERNST & YOUNG LLP, INDEPENDENT AUDITORS We consent to the reference to our firm under the captions "Selected Financial Data" and "Experts" and to the use of our report dated March 11, 1999, in the Registration Statement (Form S-1) and related Prospectus of Maxygen, Inc. for the registration of shares of its common stock. /s/ Ernst & Young LLP Palo Alto, California October 19, 1999