Management of hirsutism with high-dose oral cyproterone acetate (CPA) is associated with a failure rate of about 30%. The present investigation analyses the efficacy of parenteral CPA administration in non-tumorous hyperandrogenism. Medium-dose CPA (300 mg) was injected intramuscularly once per month, followed by oral ethinylestradiol (40 micrograms daily) for 21 days in 42 patients (total of 293 treatment cycles). The onset of withdrawal bleeding was 3 to 8 days later. This regimen was used as primary therapy (group A; n = 18) as well as follow-up therapy in low-dose (group B; n = 10) and high-dose oral standard CPA failures (group C; n = 14). The following satisfactory or good response rates were observed in regard to hirsutism: group A 83,5%, group B 100%, group C 57%; seborrhea A and B 100%, C 89%; acne and androgenetic alopecia A and B and C 100%. Clinical side effects occurred in 20 patients; they corresponded in type and frequency to those elicited by the high-dose oral standard medication and resulted in termination of treatment in only 3 patients. Pilot studies regarding the pharmacokinetics of CPA as well as the effects on plasma total and free testosterone and prolactin failed to explain the therapeutic superiority of parenteral CPA (n = 7 women). Still, it may be concluded that intramuscular CPA administration represents a new and highly effective means of managing hirsute females.