Topterone is an anti-androgen agent. Topterone inhibited stimulation of flank organ development of castrated immature male hamsters by both testosterone and dihydrotestosterone. Topical application of topterone on the flank organs of the male hamster did not cause any significant effect on testosterone metabolism of this tissue. In addition, there was no decrease in the lipogenic capacity of the flank organ. Topterone exerts its antiandrogenic action by binding with the cytosolic androgen receptor(s) in the flank organ thus inhibiting the action of dihydrotestosterone. Systemic administration demonstrated that topterone was both antiandrogenic and progestational. Topterone produced a mean inhibition of sebum excretion of 20% when it was applied topically for four weeks to the forehead skin of patients with acne.