Arrowhead Research to Report Second Quarter Fiscal 2010 Financial Results and Host Conference Call on Thursday, May 13, 2010

PASADENA, Calif. — May 7, 2010 — Arrowhead Research Corporation (NASDAQ: ARWR) today announced that it will report its financial results for the fiscal 2010 second quarter ended March 31, 2010, on Thursday, May 13, 2010, at 4:30 p.m. Eastern time (1:30 p.m. Pacific time). To participate in the conference call, please dial 877-407-4134 (toll free from the US and Canada), or 201-689-8430 (for international callers). 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 Thursday, May 20, 2010. The audio replay can be accessed by dialing 877-660-6853 (toll free from the US and Canada), or 201-612-7415 (for international callers) and entering account number 356 and passcode 350589.

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 and electronics. Arrowhead is seeking to build value for shareholders through the progress of its portfolio companies. Currently, Arrowhead is focused primarily on its two majority owned subsidiaries, Unidym, a leader in carbon nanotube technology for electronic applications, and Calando, at the forefront of clinical application of RNAi delivery technology. Arrowhead also has minority investments in two privately held nanobiotech companies.