Exhibit 23.1

CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

We consent to the reference to our firm under the caption “Experts” in the Registration Statement on Form S-3 and related Prospectus of Protein Design Labs, Inc. for the registration of 4,058,935 shares of its common stock and to the incorporation by reference therein of our reports dated March 11, 2005, with respect to the consolidated financial statements of Protein Design Labs, Inc., Protein Design Labs, Inc. management’s assessment of the effectiveness of internal control over financial reporting, and the effectiveness of internal control over financial reporting of Protein Design Labs, Inc., included in its Annual Report (Form 10-K) for the year ended December 31, 2004, filed with the Securities and Exchange Commission.

/s/ ERNST & YOUNG LLP

Palo Alto, California

September 26, 2005