Arrowhead's Warrants Delisted from Nasdaq after the Close of Business on Wednesday, June 8, 2005

PASADENA, California – (BUSINESS WIRE) – June 9, 2005 – Arrowhead Research Corporation (NASDAQ:ARWR) delisted its warrants to purchase common stock (NASDAQ:ARWRW) from The Nasdaq Stock Market after the close of business on Wednesday, June 8, 2005, as part of its previously announced Warrant Redemption plan. Warrant holders may exercise their Warrants until 4:00 PM PST on Tuesday, June 14, 2005 (the "Exercise Deadline"). The warrants are exercisable for $1.50 per share and are redeemable at the redemption price of $0.001 per warrant. Unless the Exercise Deadline is extended, Warrants not properly exercised by the Exercise Deadline will be redeemed by the Company for $0.001 per share on Wednesday, June 15, 2005.

About Arrowhead Research Corporation

Arrowhead Research Corporation (www.arrowheadresearch.com) is a publicly-traded nanotechnology company commercializing new technologies in the areas of life sciences, electronics, and energy. Arrowhead is building value for shareholders through the progress of majority owned subsidiaries founded on nanotechnologies originally developed at universities. The company works closely with universities to source early stage deals and to generate rights to intellectual property covering promising new nanotechnologies. Currently, Arrowhead has four subsidiaries commercializing nanotech products and applications, including anti-cancer drugs, RNAi therapeutics, carbon-based electronics and compound semiconductor materials.

Safe Harbor Statement under the Private Securities Litigation Reform Act of 1995:

This news release contains forward-looking statements within the meaning of the "safe harbor" provisions of the Private Securities Litigation Reform Act of 1995. These statements are based upon our current expectations and speak only as of the date hereof. Our actual results may differ materially and adversely from those expressed in any forward-looking statements as a result of various factors and uncertainties, including the recent economic slowdown affecting technology companies, the future success of our scientific studies, our ability to successfully develop products, rapid technological change in our markets, changes in demand for our future products, legislative, regulatory and competitive developments and general economic conditions. Our Annual Report on Form 10-K and 10-K/A, recent and forthcoming Quarterly Reports on Form 10-Q and 10-Q/A, recent Current Reports on Forms 8-K and 8-K/A, our Registration Statement on Form S-3, and other SEC filings discuss some of the important risk factors that may affect our business, results of operations and financial condition. We undertake no obligation to revise or update publicly any forward-looking statements for any reason.

Contacts

R. Bruce Stewart, President
Telephone: 626.792.5549
Email: bruce@arrowres.com