Chiron to Testify Today to the Value of Influenza Vaccination Before U.S. Senate Special Committee on Aging.

EMERYVILLE, Calif. -- President and CEO Howard Pien Reiterates Supply Expectations Of Fluvirin(R) Influenza Virus Vaccine as Stated in August

Chiron Corporation (Nasdaq:CHIR) announced that president and chief executive officer Howard Pien will appear before the U.S. Senate Special Committee on Aging in Washington, D.C., today in a hearing titled, "Combating the Flu: Keeping Seniors Alive." Mr. Pien will speak on the value of influenza vaccine in protecting health, the importance of raising awareness of the benefits of vaccination, and the need to prepare for an influenza pandemic.

Mr. Pien will also reiterate Chiron's expectation, as stated in the company's August 26, 2004, press release, that it will supply between 46 million and 48 million Fluvirin(R) influenza virus vaccine doses to the U.S. market for the 2004-2005 influenza season, beginning in early October. The planned late-season delivery of 2 million Fluvirin doses for a national stockpile held by the U.S. Centers for Disease Control and Prevention (CDC), not included in the totals above, remains on schedule as well. Since its August announcement, Chiron has worked closely with government agencies to keep them informed of its retesting process. The results of the confirmatory testing to date are consistent with the company's shipping expectations. Following compilation and formal sign-off of its test data, Chiron expects to complete its discussions with regulatory authorities and proceed with releasing Fluvirin to the U.S. market in early October.

A Committee announcement of today's hearing states that the CDC estimates that 6 of every 10 seniors received a flu shot last year, and that federal health officials have established a goal of vaccinating at least 90 percent of seniors by 2010. The hearing coincides with National Adult Immunization Awareness Week, which runs from September 26 through October 2.

In submitted testimony to the Committee, Mr. Pien stated, "Chiron has invested heavily in ensuring that the United States has a supply of influenza vaccine in interpandemic years, which will contribute to protecting the elderly against morbidity and mortality due to the disease. Chiron is committed to the U.S. influenza market and working with government to protect the population, as it continues to age, against influenza as well as to position the United States for preparedness for a global influenza pandemic."

As October and November are the primary months when influenza vaccine is given, the impact of Chiron's shipment delay on the 2004-2005 influenza vaccination season should be minimal. Furthermore, as in past years, the CDC urges continuation of influenza vaccination into December and beyond, given vaccine availability.

To learn more about the hearing, view it via webcast, or read the testimony, please visit http://aging.senate.gov. A live audiocast of the hearing may also be available on the C-SPAN website at http://www.capitolhearings.org. Mr. Pien's testimony will follow that of witnesses representing the CDC and the National Institute of Allergies and Infectious Disease, among others.

About Influenza and Influenza Vaccines

According to the CDC, about 5 to 20 percent of the U.S. population contracts influenza each year. Vaccination not only decreases the risk of illness for the vaccine recipient but also helps prevent the spread of the influenza virus and limits its role in the potential development of life-threatening complications. CDC statistics show that, in an average year in the United States, influenza causes more than 200,000 hospitalizations and kills 36,000 people, primarily in ages 65 and older.

Influenza, a contagious disease caused by the influenza virus, affects the respiratory tract, often resulting in symptoms in the nose, throat and lungs, as well as fever, headache, tiredness and body aches. It can also lead to complications such as pneumonia, bronchitis, or sinus and ear infections or exacerbate chronic conditions.

Influenza vaccination provides protection from influenza within about two weeks of administration and may last for as long as a year. The vaccine protects 70 to 90 percent of vaccinated people from contracting influenza, and vaccinated people who do contract influenza generally develop milder cases than unvaccinated people. Influenza vaccines, the majority of which are made from inactivated (killed) influenza strains, are updated each year to address changes in the viruses. People who are allergic to eggs, who have had a severe reaction to an influenza shot in the past, or who have previously developed Guillain-Barre syndrome in the six weeks after receiving an influenza vaccination should consult their doctors before receiving influenza vaccination.

Important Safety Information for Fluvirin(R) Influenza Virus Vaccine

The most common side effect of vaccination with Fluvirin is soreness at the injection site. Less common side effects include fever, malaise, myalgia and allergic reactions. Fluvirin should not be administered to anyone with a history of hypersensitivity to any component of the vaccine, including eggs, egg products or thimerosal. As is the case with most drugs and vaccines, there is a chance that a serious allergic reaction, serious illness or even death could occur as a result of vaccination with Fluvirin. Generally, persons should not be vaccinated during an acute febrile illness. Fluvirin is not indicated for children under 4 years of age. Persons should consult with their healthcare providers if they are pregnant and/or are taking other medications. Fluvirin may not protect 100 percent of individuals who are susceptible to influenza. Before administering Fluvirin, please see full prescribing information. For more information about Fluvirin, please visit www.chiron.com/fluvirin or call [phone].

About Chiron

Through its global Blood Testing, Vaccines and BioPharmaceuticals businesses, Chiron Corporation addresses human suffering with more than 50 diverse products to detect, prevent and treat disease worldwide. The company's consistent success has come from its pioneering science, skill in delivering innovations in biotechnology and disciplined business approach. Chiron believes that science has the power to improve people's lives and harnesses that power to transform human health. For more information about Chiron, please visit www.chiron.com.

About Chiron Vaccines

Chiron Vaccines, the world's fifth-largest vaccines business, is headquartered in Oxford, United Kingdom, and has facilities located throughout Europe, the United States and Asia. Chiron Vaccines is the world's second-largest manufacturer of influenza vaccines and has important meningitis, pediatric and travel vaccine franchises. Chiron Vaccines is the leading vaccine manufacturer in the United Kingdom, Germany and Italy. The company's portfolio of products includes vaccines for influenza, meningitis C, rabies, tick-borne encephalitis, yellow fever, haemophilus influenzae B (Hib), polio, mumps, measles and rubella (MMR) and diphtheria, tetanus and pertussis (whooping cough).

This year, Chiron Vaccines celebrates 100 years of advancing medicine with the anniversary of two founding companies. In 1904, Emil von Behring and Achille Sclavo independently started companies in Germany and Italy, respectively, dedicated to the research, development and manufacture of vaccines to protect humanity from infectious disease. As the fifth-largest vaccine manufacturer in the world, Chiron remains dedicated to the legacies of von Behring and Sclavo to prevent disease and develop new vaccines to improve human health globally.

This news release contains forward-looking statements, including statements regarding the amount of doses of Fluvirin that Chiron expects to deliver to the U.S. market and the timing of the delivery of those doses both in aggregate and with respect to the doses for the CDC's national stockpile. These forward-looking statements involve risks and uncertainties and are subject to change. No assurances can be given that additional sterility or delivery issues with respect to Fluvirin will not arise in the future. Many factors could cause actual results and developments to differ materially from those expressed or implied by these forward-looking statements, including, among others, additional adverse developments resulting from the completion of Chiron's additional tests and investigations or discussions with or actions taken or required by regulatory agencies. In addition, 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-Q for the quarter ended June 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 other important factors that could cause the company's actual performance to differ from the expectation expressed or implied by these forward-looking statements, including the outcome of clinical trials, regulatory review and approvals, manufacturing and testing capabilities, pricing pressures, intellectual property protections and defenses, litigation, stock-price volatility, and marketing effectiveness. In particular, there can be no assurance that Chiron will timely ship and release Fluvirin, maintain anticipated levels of profitability, increase sales of existing products, successfully develop and receive approval to market new products, or achieve market acceptance for such new products. In addition, the company 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.

Consistent with SEC Regulation FD, we do not undertake an obligation to update the forward-looking information we are giving today.

NOTE: Fluvirin is a trademark of Chiron Corporation.