Arrowhead Research to Report Fiscal 2009 Fourth Quarter and Year-End Financial Results and Host Conference Call on Tuesday, December 22, 2009

PASADENA, Calif. — December 21, 2009 — Arrowhead Research Corporation (NASDAQ: ARWR) today announced that it will report its financial results for the fiscal 2009 fourth quarter and year ended September 30, 2009, on Tuesday, December 22, 2009 at 4:30 p.m. Eastern time (1:30 p.m. Pacific time). To participate in the conference call, please dial 877-941-2068 or 480-629-9712. Investors may also access a live audio webcast of this conference call on the Company's website at www.arrowheadresearch.com.

A replay of the webcast will be available approximately two hours after the conclusion of the call. The webcast archive will remain available for 90 days. An audio replay will also be available approximately two hours after the conclusion of the call and will be made available until Tuesday, January 5, 2010. The audio replay can be accessed by dialing 800-406-7325 or 303-590-3030 and entering passcode 4196542#.

About Arrowhead Research Corporation

Arrowhead Research Corporation (www.arrowheadresearch.com) (NASDAQ: ARWR) is a nanotechnology company commercializing new technologies in the areas of life sciences, electronics, and energy. Arrowhead is seeking to build value for shareholders through the progress of majority owned subsidiaries. Currently, Arrowhead has four subsidiaries commercializing nanotech products and applications and minority investments in two privately held nanobiotech companies.