FDA Requests Additional Data on PULMINIQ(TM) (Cyclosporine, USP) Inhalation Solution; Agency Action Letter States that PULMINIQ

Chiron Corporation (NASDAQ:CHIR) today announced that
the company has received an action letter from the U.S. Food and Drug
Administration (FDA) stating that the company's New Drug Application
(NDA) for PULMINIQ(TM) (cyclosporine, USP) inhalation solution is
"approvable" but that an additional pre-approval study is required to
confirm the efficacy of the drug. In the NDA for PULMINIQ, Chiron is
seeking an indication to increase survival and prevent chronic
rejection in patients receiving allogeneic lung transplants, in
combination with standard immunosuppressive therapy. Chiron is
evaluating possible next steps for PULMINIQ.
   "Chiron in-licensed PULMINIQ knowing the significant regulatory
challenges associated with a single-center trial with a small patient
population. We took on these challenges because we believe strongly in
the data for PULMINIQ," said Craig Wheeler, president, Chiron
BioPharmaceuticals. "We will carefully review our options before
making any decisions regarding the product."

   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 regulatory review and approval, that involve
risks and uncertainties and are subject to change. Forward-looking
statements often address our expected future performance and often
contain words such as "expects," "anticipates," "intends," "plans,"
"believes," "seeks" or "will." 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,
regulatory review and approvals, manufacturing capabilities,
intellectual property protections and defenses, litigation,
stock-price and interest-rate volatility, marketing effectiveness,
additional adverse developments resulting from the suspension of
Chiron's UK license to manufacture FLUVIRIN(R) influenza virus vaccine
from October 5, 2004, through March 2, 2005, the announcement of such
suspension and the litigation and investigations relating to those
matters. In addition, the company may engage in business
opportunities, the successful completion of which is subject to
certain risks, including approval by Novartis AG, regulatory
approvals, and the integration of operations.
   Chiron does not undertake an obligation to update the
forward-looking information the company is giving today.

   Note: FLUVIRIN and PULMINIQ are trademarks of Chiron Corporation.