Chiron Signs Contract with South African National Blood Service.

EMERYVILLE, Calif. -- One Million Whole Blood Donations to Be Screened Annually Using Fully Automated PROCLEIX(R) TIGRIS(R) System with the PROCLEIX(R) ULTRIO(TM) Assay

Chiron Corporation (Nasdaq:CHIR) today announced that the South African National Blood Service (SANBS) plans to initiate testing of whole blood donations using the fully automated PROCLEIX(R) TIGRIS(R) System with the PROCLEIX(R) ULTRIO(TM) Assay beginning in September 2005. The donations, which are expected to total approximately 800,000 units annually, will be screened individually for HIV-1, hepatitis C and hepatitis B. Financial terms of the agreement were not disclosed. In addition, the Western Province Blood Transfusion Service (WPBTS) in South Africa plans to initiate nucleic acid testing (NAT) in September with the PROCLEIX ULTRIO Assay, screening another 200,000 units annually. Chiron's NAT products are distributed in South Africa by Ilex Medical Ltd.

"This agreement highlights the powerful combination that the PROCLEIX TIGRIS System and the PROCLEIX ULTRIO Assay represent for global blood safety," said Gene Walther, president, Chiron Blood Testing. "Adoption of the PROCLEIX ULTRIO Assay has been strong in existing markets and is helping to drive geographic expansion of our business. We look forward to working with SANBS to protect health by improving the safety of the South African blood supply."

"The implementation of the PROCLEIX TIGRIS System will add significantly to the safety of the South African blood supply. This system will be key to our risk management model and will minimize the residual window period risk of a transfusion in our country with a high incidence, particularly of HIV/AIDS and hepatitis B. We look forward to working with Chiron and Ilex Medical Ltd.," said Professor Anthon Heyns, the chief executive officer of SANBS.

"This endeavor is the most exciting project I have experienced in decades in our industry," said Dr. Moshe Benshaul, chief executive officer of Ilex. "The challenge to implement NAT in the entire country within such a short period is feasible due to the commitment of the highly motivated professional team of SANBS. Routine use of NAT in blood screening will have a far reaching impact not only for the health of the South African community, but also for the whole region."

The PROCLEIX TIGRIS System and the PROCLEIX ULTRIO Assay were developed in collaboration with Gen-Probe Incorporated. The fully automated, high-throughput PROCLEIX TIGRIS System can process 1,000 tubes in under 14 hours, facilitating testing in smaller pool sizes and individual donor testing. The PROCLEIX ULTRIO Assay is designed to detect the presence of all known HIV-1 groups and subtypes and HCV and HBV genotypes during the very early stages of infection, when these agents cannot be detected by immunodiagnostic tests. Use of the PROCLEIX TIGRIS System for the PROCLEIX ULTRIO Assay enables individual donor testing, which is the most sensitive method of screening blood donations currently available.

About PROCLEIX(R) Assays and Systems

PROCLEIX(R) Assays and Systems incorporate state-of-the-art NAT technology to detect viral RNA and DNA in donated blood and plasma during the very early stages of infection, when those infectious agents are present but cannot be detected by immunodiagnostic tests. The PROCLEIX(R) HIV-1/HCV Assay, developed in collaboration with Gen-Probe Incorporated, has been commercially available in Europe since 1999 and also bears the CE Mark. The PROCLEIX HIV-1/HCV Assay is approved for use in the United States, the European Union, Australia and major markets in Asia. The PROCLEIX(R) Ultrio(TM) Assay for the simultaneous detection of HIV-1, HCV and HBV has been commercially available in Europe since early 2004 and also bears the CE Mark. For more information about Chiron Blood Testing, visit www.eBloodBank.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.

This news release contains forward-looking statements, including statements regarding sales growth, product development initiatives, new product indications, new product marketing, acquisitions, and in- and out-licensing activities that involve risks and uncertainties and are subject to change. A full discussion of the company's operations and financial condition, including factors that may affect its business and future prospects, is contained in documents the company has filed with the SEC, including the form 10-K for the year ended December 31, 2004, and will be contained in all subsequent periodic filings made with the SEC. These documents identify important factors that could cause the company's actual performance to differ from current expectations, including 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. In particular, there can be no assurance that Chiron will increase sales of existing products, successfully develop and receive approval to market new products, or achieve market acceptance for such new products. 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.

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

Note: PROCLEIX and ULTRIO are trademarks of Chiron Corporation. TIGRIS is a registered trademark of Gen-Probe Incorporated.