The antiandrogen cyproterone acetate, which is known to suppress sebum production, but is not a standard therapy, was given in combination with tetracycline to 63 young unmarried men who had failed to respond to 6 months' tetracycline therapy alone. Fifty-seven patients responded and the mean time to clearance was 5.2 months' therapy. The main side effects were nodular sub-nipple breast swellings, which occurred in 13 cases (21%). Such side effects were reversible and cleared after 3-4 months following cessation of therapy. Eighty-eight percent of patients relapsed within 3 months of discontinuing therapy.