Arrowhead Research to Report Fiscal 2011 Second Quarter Financial Results and Host Conference Call on Thursday, May 12, 2011

PASADENA, Calif. — May 4, 2011 — Arrowhead Research Corporation (NASDAQ: ARWR), a nanomedicine company with development programs in oncology, obesity and regenerative medicine, today announced that it will report its financial results for the fiscal 2011 second quarter ended March 31, 2011, on Thursday, May 12, 2011 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 19, 2011. 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 371945.

About Arrowhead Research Corporation

Arrowhead Research Corporation (NASDAQ: ARWR) is a nanomedicine company developing innovative therapeutic products at the interface of biology and nanoengineering to cure disease and improve human health. Arrowhead addresses its target markets through focused subsidiaries, which include: Calando Pharmaceuticals, a leader in delivering small RNAs for gene silencing; Ablaris Therapeutics, an anti-obesity therapeutics company; and Nanotope, a regenerative medicine company. For more information please visit http://www.arrowheadresearch.com.