In an open therapeutic trial, 50 patients with acne vulgaris were randomly allocated to one of two groups. One group received spironolactone 100 mg daily and the other cimetidine 1.6 g daily for 12 weeks. Clinical severity of acne and sebum excretion decreased significantly at the end of the trial with both drugs, but significantly more with spironolactone. Mean serum levels of testosterone, androstenedione and dehydroepiandrosterone-sulfate decreased significantly with spironolactone but showed no change with cimetidine. Our data suggest that spironolactone may be useful as antiandrogen in the short term therapy of acne vulgaris.