To compare the efficacy of a 3-month trial of leuprolide acetate (LA; Lupron; TAP Pharmaceuticals, Deerfield, IL) versus danazol (Danocrine; Scenofi Winthrup Pharmaceuticals, New York, NY) therapy on laparoscopically proven endometriosis. Endometriosis severity was assessed at the time of laparoscopy and patients were randomized to receive 0.1 mg SC LA (n = 22) or 800 mg danazol orally (n = 18) daily for 3 months. A second laparoscopy and/or laparotomy was performed to assess the change in the extent of endometriosis and for surgical therapy. Private practice at a university-affiliated hospital. Forty patients with mild, moderate, or severe endometriosis. Ten patients were excluded. Three-month treatment randomly assigned to either LA or danazol. Prospective measurement of American Fertility Society endometriosis scores and size of ovarian endometriomata before and after therapy via laparoscopy. The mean endometriosis score including adhesions decreased significantly from 36 ± 4.9 to 29 ± 5.0 (mean ± SEM) with LA and from 34 ± 6.4 to 29 ± 6.5 with danazol. The mean laparoscopic endometriosis score not including adhesions decreased from 27 ± 3.5 to 22 ± 3.4 with LA and 22 ± 3.5 to 19 ± 3.1 with danazol. Seven of 18 (39%) endometriomata responded to LA and 6 of 15 (40%) endometriomata responded to danazol. We conclude that both danazol and LA will reduce endometriosis scores after a 3-month course of therapy. Larger clinical trials are needed to compare short courses of therapy with the more established 6-month trials. A 3-month versus a 6-month course of therapy offers obvious benefits including decreased cost and decreased side effects.