EXHIBIT 10.509

                        DESCRIPTION OF CHIRON CORPORATION'S
               1999 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
five-member Compensation Committee of the Board of Directors.

For 1999, 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 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.