A randomized cross-over study was done to compare the therapeutic efficacy of cyproterone acetate (CPA, 50 mg/day orally) and a depot preparation of the LHRH super-agonist ( D-Trp<sup>6</sup> LHRH 3 mg i.m. once a month) in 10 patients with polycystic ovarian disease (PCO). The two treatment periods were separated by 6 months. Both treatments resulted in marked clinical improvement. In response to CPA treatment, basal plasma gonadotropin, estradiol, estrone, testosterone and androstenedione levels significantly decreased. In response to D-Trp<sup>6</sup> LHRH, both basal and stimulated gonadotropin levels were completely suppressed after 3 weeks of treatment. After initial elevation on day 2, plasma ovarian steroid levels fell into the castrate range, without any change in dehydroepiandrosterone sulfate levels. Urinary 3α-androstanediol excretion decreased significantly. In patients with PCO, LHRH-A induced more complete gonadotropin inhibition than did CPA. However, following cessation of either therapy, the disease rapidly recurred.