Chiron and Cubist Pharmaceuticals Announce the Filing for EU Regulatory Approval to Market Cubicin -Daptomycin for Injection-.

EMERYVILLE, Calif. & LEXINGTON, Mass. -- Filing Moves CUBICIN Closer to EU Commercialization

Chiron Corporation (Nasdaq:CHIR) and Cubist Pharmaceuticals, Inc. (Nasdaq:CBST) today announced that Chiron has submitted a Marketing Authorization

Application (MAA) to the European Medicines Agency (EMEA) under the European Union's Centralized Procedure for approval to market CUBICIN(R) (daptomycin for injection). The indication in the submission is for complicated skin and soft-tissue infections (cSSTI) where the presence of susceptible Gram-positive bacteria is confirmed or suspected. The filing includes safety data from two pivotal Phase 3 clinical trials conducted by Cubist that examined the safety and efficacy of CUBICIN in the treatment of cSSSI.

"This filing is a crucial step toward our goal of launching CUBICIN in the European Union," said Craig Wheeler, president, Chiron BioPharmaceuticals. "Approval to market CUBICIN would expand our portfolio of anti-infective products and allow us to leverage our existing sales and marketing force in the European Union to bring a potentially important new product to patients."

Michael W. Bonney, President and CEO of Cubist, added, "This filing is an important milestone in Cubist's partnership with Chiron. The two companies have worked closely and effectively to make this happen on schedule. We look forward to supporting Chiron through the European Review cycle and, if approved, in their launch of CUBICIN in the second largest market place for this drug, the EU."

As a result of the filing, the EMEA Committee for Medicinal Products for Human Use (CHMP) will evaluate the application to determine whether to approve the marketing of CUBICIN in all 25 member states of the European Union. In October 2003, Cubist and Chiron completed a license agreement for the development and commercialization of CUBICIN in Western and Eastern Europe, Australia, New Zealand, India and certain Central American, South American and Middle Eastern countries. Under the terms of the agreement, Chiron is responsible for regulatory filings in those territories.

About CUBICIN(R) (Daptomycin for Injection)

CUBICIN is currently the only once-daily bactericidal antibiotic approved in the United States indicated for the treatment of complicated skin and skin-structure infections caused by susceptible strains of the following Gram-positive microorganisms: Staphylococcus aureus (including methicillin-resistant strains), Streptococcus pyogenes, S. agalactiae, S. dysgalactiae subsp equisimilis and Enterococcus faecalis (vancomycin-susceptible strains only). CUBICIN is not indicated for the treatment of pneumonia. Most adverse events reported in clinical trials were mild or moderate in intensity, and the most common were constipation, nausea, injection site reactions and headache. To reduce the development of drug-resistant bacteria and maintain the effectiveness of CUBICIN, CUBICIN should be used only to treat or prevent infections that are proven or strongly suspected to be caused by bacteria susceptible to CUBICIN. For full prescribing information, visit www.Cubicin.com.

About Chiron

Chiron delivers innovative and valuable products to protect human health by advancing pioneering science across the landscape of biotechnology. The company works to deliver on the limitless promise of science and make a positive difference in people's lives. For more information about Chiron, please visit www.chiron.com.

About Cubist

Cubist Pharmaceuticals, Inc. is a biopharmaceutical company focused on the research, development and commercialization of antiinfective products that meet unmet medical needs. In the U.S., Cubist markets CUBICIN(R) (daptomycin for injection), the first antibiotic in a new class of antiinfectives called lipopeptides. Cubist's pipeline includes HepeX-B(TM), a monoclonal antibody biologic currently in the second of two Phase 2 trials to determine its potential for the prevention of infection by the Hepatitis B virus (HBV) in liver transplant patients, and research efforts focused on novel members of the lipopeptide class of molecules. Cubist is headquartered in Lexington, MA.

Chiron Safe Harbor Statement

This news release contains forward-looking statements, including statements regarding filings seeking approval to market, and the subsequent commercialization and potential sales of, CUBICIN(R) (daptomycin for injection), that involve risks and uncertainties and are subject to change. A full discussion of Chiron's operations and financial condition, including factors that may affect its business and future prospects generally, is contained in documents the company has filed with the SEC, including the form 10-Q for the quarter ended September 30, 2004, and the form 10-K for the year ended December 31, 2003, and will be contained in all subsequent periodic filings made with the SEC. These documents identify important factors that could cause Chiron's actual performance to differ materially from current expectations, including those expressed or implied by the forward-looking statements included in this press release. In particular, there can be no assurance (1) that Chiron will receive approval to market CUBICIN in the European Union, (2) that CUBICIN will achieve acceptance by physicians, patients, third-party payors or the medical community generally or with respect to the level of such acceptance, (3) that Cubist will be able to successfully manufacture CUBICIN on a commercial scale, or (4) that Chiron will successfully commercialize CUBICIN in Europe as well as in the U.S. or that other parties will not successfully commercialize products that are competitive with CUBICIN. Other factors include the outcome of clinical trials, regulatory review and approvals, manufacturing capabilities, intellectual property protections and defenses, stock-price and interest-rate volatility, and marketing effectiveness. There can be no assurance that Chiron's out-licensing activities will generate significant revenue, nor that its in-licensing activities will fully protect it from claims of infringement by third parties. In addition, Chiron may engage in business opportunities, the successful completion of which are subject to certain risks, including shareholder and regulatory approvals and the integration of operations.

We do not undertake an obligation to update the forward-looking information we are giving today.

Cubist Safe Harbor Statement

Statements contained herein that are not historical fact may be forward-looking statements within the meaning of Section 27A of the Securities Act of 1933 and Section 21E of the Securities Exchange Act of 1934, and such statements are subject to a variety of risks and uncertainties. There are a number of important factors that could cause actual results to differ materially from those projected or suggested in any forward-looking statements made by Cubist. These factors include, but are not limited to: (i) the level of acceptance of CUBICIN by physicians, patients, third-party payors, and the medical community generally; (ii) Cubist's ability to continue to develop, secure additional regulatory approvals for, and successfully market, CUBICIN; (iii) Cubist's ability to manufacture CUBICIN on a commercial scale; (iv) commercialization of products that are competitive with CUBICIN; (v) Cubist's ability to discover or in-license drug candidates; (vi) Cubist's ability to successfully develop drug candidates in its pipeline, including HepeX-B; (vii) Cubist's ability to successfully commercialize any product or technology developed by Cubist; (viii) Cubist's ability to establish and maintain successful manufacturing, sales and marketing, distribution, and development collaborations; (ix) legislative or regulatory changes adversely affecting Cubist or the biopharmaceutical industry; (x) Cubist's ability to protect its intellectual property and proprietary technologies; and (xi) Cubist's ability to finance its operations. Additional factors that could cause actual results to differ materially from those projected or suggested in any forward-looking statements are contained in Cubist's recent filings with the Securities and Exchange Commission, including those factors discussed under the caption "Risk Factors" in such filings.

Cubist and CUBICIN are registered trademarks of Cubist Pharmaceuticals, Inc.; HepeX-B is a trademark of XTL Biopharmaceuticals Ltd.

Additional information can be found at Cubist's web site at www.cubist.com.