text: Cyproterone acetate is a 6-chloro-1,2-methylene derivative of 17α-acetoxyprogesterone. It shows major antiandrogenic activity together with androgenic activities. Cyproterone acetate displays high affinity for AR in rats which increases when the 1,2-methylene group is removed from the compound. If the chlorine atom is replaced by a methyl group the binding slightly decreases, whereas further removal of the C6 double bond modifies the binding kinetics, see figure 7.