18 patients with obstructive benign prostatic hypertrophy were studied. A 5-day treatment with gestonorone caproate (200 mg daily and 200 mg on alternate days) and cyproterone acetate (300 mg daily) suppressed the plasma LH and serum LH levels. Subsequently, H3-testosterone was injected intravenously and its elimination from plasma and uptake and metabolism in the BPH tissue studied. The elimination of total radioactivity and H3-testosterone from plasma was not altered after the 3 treatment regimens as compared to the control group. The uptake of total radioactivity into BPH tissue and its intraprostatic metabolism particularly to dihydrotestosterone was significantly suppressed in the patients with daily injections of gestonorone. Cyproterone acetate and gestonorone caproate on alternate days did not cause this effect.