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PRESS RELEASE
June 28, 2007

Arrowhead Upgrades Listing to NASDAQ Global Market

PASADENA, California – June 28, 2007 – Arrowhead Research Corporation (NASDAQ:ARWR) announced today that the NASDAQ Stock Market has approved its application for upgrading its listing to the NASDAQ Global MarketSM, formerly known as the NASDAQ National Market. Arrowhead expects to commence trading on the NASDAQ Global Market on Friday, June 29, 2007 under its current symbol, “ARWR.”

“Meeting the more stringent requirements for a NASDAQ Global Market listing is representative of the progress Arrowhead is making in building value for shareholders,” said R. Bruce Stewart, Arrowhead’s Chairman. “We are confident that the listing will generate even broader market exposure for the company.”

The NASDAQ Global Market consists of over 1,450 companies that have applied for listing, having met and continued to meet stringent financial and liquidity requirements and agreed to meet specific corporate governance standards. Formerly called The NASDAQ National Market, this market was renamed in 2006 to reflect the global leadership and international reach of this market and the companies whose securities are listed there.

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.

About NASDAQ

The NASDAQ Stock Market® is the largest U.S. electronic stock market and the fastest, most emulated market model worldwide. Approximately 3,200 companies from 37 countries and across all industry sectors are listed here. NASDAQ® lists more companies, on average, trades more shares per day — about two-billion shares daily — and handles more IPOs — over 1,000 since 2000 — than any other U.S. exchange. NASDAQ delivers the highest regulatory integrity and a robust body of high-value services for companies at all stages of public ownership.

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

Virginia Dadey; Vice President, Investor Relations
Telephone: 212.541.3707
Email: vdadey@arrowres.com