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EXHIBIT 10.509

DESCRIPTION OF CHIRON CORPORATION'S
2001 EXECUTIVE OFFICERS VARIABLE COMPENSATION PROGRAM

Decisions on compensation (base salary and variable compensation) of Chiron
Corporation's ('Chiron' or the 'Company') executive officers are made by the
Compensation Committee of the Board of Directors.

For 2001, the Compensation Committee continued the Company's approach that base
salaries for executive officers should be measured by reference to the median
(50th percentile) of salaries for benchmark positions in comparator companies.
Further, the Compensation Committee provided that a significant portion of total
cash compensation (salary plus variable compensation) in the form of annual
variable cash compensation potential should be 'at risk,' dependent upon
individual, business unit and overall Company performance. Variable cash
compensation for executive officers overall was targeted to yield total cash
compensation at the 50% percentile, but with the opportunity to significantly
exceed the 50% percentile of total cash compensation as shown by comparative
data, in the case of outstanding Company, business unit, and individual
performance.

The Compensation Committee based its decisions regarding variable compensation
for executive officers upon its evaluation of performance against
pre-established performance metrics developed at the Company, business unit and
functional or corporate unit level.

Variable compensation for the Chairman and Chief Executive Officer is based on
the performance of the Company as measured against the pre-established Company
metrics composed of financial objectives and technology and business innovation
milestones.

Executive officers responsible for business units or major functional or
corporate units are eligible for variable compensation based on the
pre-established Company metrics and on the achievement of their respective
business, functional, or corporate unit metrics.

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DESCRIPTION OF CHIRON CORPORATION'S 2001 EXECUTIVE OFFICERS VARIABLE
COMPENSATION PROGRAM