A randomized cross-over study was done to compare the therapeutic efficacy of cyproterone acetate (CPA) and a depot preparation of the LHRH superagonist (DTrp6-LHRH) in 10 patients with polycystic ovarian disease (PCO). All patients were treated with both agents (50 mg/day CPA, orally and (3 mg DTrp6-LHRH, im, approximately once a month) for 3 months, the 2 treatment periods being separated by 6 months. Both treatments resulted in marked clinical improvement, with diminished acne and seborrhoea and normalization of ovarian size by ultrasonographic criteria. In response to CPA treatment, basal plasma gonadotropin levels decreased, but the response to a LHRH test was not completely suppressed. Plasma estradiol, estrone, testosterone, and androstenedione levels significantly decreased, but urinary 3 alpha-androstanediol and plasma dehydroepiandrosterone sulfate levels did not change significantly. In contrast to CPA treatment, both basal and stimulated gonadotropin levels were completely suppressed after 3 weeks of treatment with DTrp6-LHRH. After a slight initial evaluation on day 2, plasma estrogen and androgen levels, with the exception of dehydroepiandrosterone sulfate fell into the castrate range urinary 3 alpha-androstanediol excretion decreased significantly. Thus, in patients with PCO, LHRH-A induced more complete gonadotropin inhibition than did CPA. After cessation of either therapy, the disease rapidly recurred.