ARROWHEAD ANNOUNCES OFFERING OF COMMON STOCK AND WARRANTS

Pasadena, CA – June 17, 2010 – Arrowhead Research Corporation (NASDAQ: ARWR) today announced that it has priced and received firm commitments for a registered direct offering to raise $8.65 million through the sale of 6.6 million shares of its common stock, and warrants to purchase 3.3 million shares of common stock. The stock and warrants will be sold in units, at a price of $1.312 per unit, with each unit consisting of one share of common stock and a warrant to purchase one-half of one share of common stock. Oppenheimer & Co. Inc. is acting as the sole placement agent for the offering. Use of proceeds includes additional investments in current subsidiaries, new investments, and operating expenses. The closing is expected to take place on or about June 22, 2010, subject to the satisfaction of customary closing conditions.

The warrants have an exercise price of $1.65 per share of common stock, with an exercise term of five years, and are exercisable commencing 6 months following the closing of the offering.

The securities will be issued under Arrowhead’s shelf registration statement filed on Form S-3, which was declared effective by the Securities and Exchange Commission on June 11, 2010. The final prospectus supplement related to this offering will be filed with the Securities and Exchange Commission.

This press release does not constitute an offer to sell or a solicitation of an offer to buy the securities referred to herein, nor shall there be any sale of these securities in any state in which such an offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such state.

The prospectus, forming part of the effective registration statement, and prospectus supplement relating to this offering contain this and other information about the Company. The offering is being made only by means of the prospectus and the related prospectus supplement, copies of which may be obtained from Oppenheimer & Co. Inc., Attn: Syndicate Prospectus Department, 300 Madison Ave., 4th Floor, New York, New York 10017, Phone (212) 667-8563, Fax (212) 667-6141, or EquityProspectus@opco.com.

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.