Arrowhead Research Corporation Named to Merrill Lynch Nanotech Index

PASADENA, Calif.--(BUSINESS WIRE)--Dec. 20, 2004--Arrowhead Research Corporation (NASDAQ:ARWR)(NASDAQ:ARWRW) announced today that the Company is now on Merrill Lynch's Nanotechnology Index (NNZ). Arrowhead is the only new addition to the Index for this quarter. "To be recognized by Merrill Lynch for inclusion in the Index is an important achievement for us. We have a unique and exciting story to tell about the commercialization of nanotechnology and have made extraordinary progress in 2004," stated R. Bruce Stewart, Arrowhead's President. "Being on the Index sets the stage for us to share this story with a wider audience in 2005."

Merrill Lynch describes the Nanotechnology Index as a diversified representation of nanotechnology stocks and ADRs traded in the United States. The Index is an equally-weighted index comprised of 26 nanotechnology stocks.

“To be recognized by Merrill Lynch for inclusion in the Index is an important achievement for us. We have a unique and exciting story to tell about the commercialization of nanotechnology and have made extraordinary progress in 2004”

About Arrowhead Research Corporation

Arrowhead Research is a diversified, development stage nanotechnology company structured to bring together an innovative mix of technologies, a broad suite of intellectual property, and some of the most respected minds in this dynamic field. There are three strategic components to Arrowhead's business model:

-- The Commercialization Program: Arrowhead forms or acquires majority-owned subsidiary companies pursuing products based on nanotechnology in high-growth technology markets.

-- The Research Program: Arrowhead funds nanoscience research at universities in exchange for the option to exclusively license the technology.

-- The IP Toolbox: Arrowhead acquires, licenses, and sublicenses intellectual property in nanotechnology.

Arrowhead Research operates three majority-owned subsidiary companies:

-- Aonex Technologies, Inc., developing and commercializing proprietary semiconductor nanomaterial technology.

-- Insert Therapeutics, Inc., developing and commercializing a proprietary nanoscale drug delivery system.

-- Nanotechnica, Inc., developing capabilities for mass production of a variety of proprietary nanoscale devices and systems, with an initial focus on tools and sensors.

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, 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 Registration Statement on Form S-3, 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, 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.