A pharmacokinetic evaluation of medroxyprogesterone acetate (MAP, 6 alpha-methyl-17 alpha-hydroxyprogesterone acetate) was undertaken in 70 patients with advanced cancer treated either orally or im with single high doses. MAP plasma levels were determined by gas chromatography (63Ni electron capture detector) after derivatization with heptafluorobutyric anhydride, using 17 alpha-hydroxyprogesterone caproate as internal standard. Plasma levels after oral administration can be approximated by a triexponential function in agreement with a pharmacokinetic two-compartment open model with first-order absorption; peak levels are dose-related, but high interindividual variance is present. Following the administration, both decay phases are masked by prolonged absorption; peak levels are lower than after oral administration, but long-term bioavailability is higher, as demonstrated by comparison of the values for areas under curves in the 0-146-hour interval. The high interindividual ranges in the observed MAP plasma levels indicate that if any significant clinical evaluation is to be made, routine analysis of plasma MAP is mandatory.