strongly on the electronic features of the substituents. Oppenauer oxidation of 3beta-hydroxy-17beta-exo-heterocyclic steroids 5a-e and 6a-e yielded the corresponding Delta(4)-3-ketosteroids 9a-e and 10a-e. The inhibitory effects (IC(50)) of these compounds on rat testicular C(17,20)-lyase were investigated by means of an in vitro radioligand incubation technique.