Chiron's Chief Scientific Officer Elected to National Academy of Sciences; Academy Recognizes Rino Rappuoli's Vaccines Work.

EMERYVILLE, Calif. -- Chiron Corporation (NASDAQ:CHIR) announced today that the National Academy of Sciences (NAS), at its annual meeting last week, elected Rino Rappuoli, Ph.D., for membership in the academy as a foreign associate. Dr. Rappuoli, chief scientific officer of Chiron and head of research for Chiron Vaccines, was named along with 17 other foreign associates and 72 new U.S. members. NAS, a private, non-profit society established in 1863, now has 1,976 active members and 360 foreign associates.

Election to NAS recognizes distinguished and continuing achievements in original research and is considered one of the highest honors a scientist or engineer can receive. NAS and the National Academy of Engineering, the Institute of Medicine and the National Research Council collectively form the National Academies, which advise the federal government on science, engineering and medicine.

"Rino's work represents Chiron's ongoing commitment to protecting people through innovative science, and we are deeply honored to see him join two of our founders, Bill Rutter and Ed Penhoet, as a member of the National Academies," said Howard Pien, CEO of Chiron. "By recognizing Rino, NAS pays tribute to the millions of lives that have been touched by vaccines developed as a result of Rino's dedication."

Dr. Rappuoli is known globally for his work in vaccines and immunology. He co-founded the field of cellular microbiology, a discipline combining cell biology and microbiology, and pioneered the genomic approach to vaccine development known as reverse vaccinology. He led Chiron's development of adjuvanted influenza vaccines, MENJUGATE(R) conjugate vaccine against meningococcal C disease and the first recombinant bacterial vaccine against pertussis. Currently, Dr. Rappuoli is actively involved in the research and development of further vaccines against meningococcal disease and avian and pandemic influenza.

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 development of vaccines against meningococcal disease and avian and pandemic influenza by Chiron. A discussion of the company's operations and financial condition, including factors that may affect its business and future prospects that could cause actual results and developments to differ materially from those expressed or implied by forward-looking statements, is contained in documents the company has filed with the SEC, including the Form 10-K for the year ended December 31, 2004, and the Form 10-Q for the quarter ended March 31, 2005, 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, among others, the outcome of clinical trials, and regulatory review and approvals.

Chiron does not undertake an obligation to update the forward-looking information it is giving today.