EXHIBIT 10.509

                        DESCRIPTION OF CHIRON CORPORATION'S
               1998 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 1998, 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.