Thirty-four patients with hirsutism were treated for 9 months with 100 mg cyproterone acetate (CA) given on days 5-15 of the menstrual cycle together with a combination oral contraceptive containing 2 mg CA and 50 micrograms ethinyloestradiol (Diane) given on days 5-25 of the cycle. After 9 months treatment patients were randomised to a 12 month double-blind cross-over trial comparing Diane plus 25 mg CA with Diane plus placebo, to test the efficacy of low-dose CA as maintenance therapy. Thirty-one patients (92%) experienced moderate or good subjective improvement in hirsutism on high-dose CA, associated with a 40% mean overall improvement in objective hirsutism grade and 13% overall reduction in hair growth rate measured by a photographic technique. Minor or moderate side effects were experienced by 64% of patients and severe side effects by 11% at this dosage. There was a mean subjective relapse rate of 33% when patients were changed to low dose CA, and relapse rates were not significantly different between the two regimens with 28% relapsing on 25 mg CA + Diane and 48% on placebo and Diane (P less than 0.05). Despite significant subjective relapse with low-dose treatment there was no significant deterioration in objective hirsutism grade or hair growth rate determined photographically. Levels of plasma testosterone, sex hormone binding globulin, free testosterone (derived) and androstenedione fell significantly on high dose CA and this reduction was maintained during low dose therapy.(ABSTRACT TRUNCATED AT 250 WORDS)