In an open, non-randomized prospective phase-III-study the clinical and endocrine efficacy as well as the safety of leuprorelin acetate depot (Enantone-Gyn Monats-Depot) were investigated. The therapeutic results of 198 patients, gathered from 5 university institutions and two city hospitals, are reported. Endometriosis was classified by the revised American Fertility Society score (r-AFS) before and at the end of treatment. Serum levels of LH, FSH, prolactin, estradiol, progesterone, androstenedione, testosterone and leuprorelin acetate were determined by radioimmunoassay. The mean total r-AFS score changed as follows: before surgical intervention during first-look laparoscopy 21 +/- 24 at the end of first-look laparoscopy 15 +/- 19 at the end of the GnRH-treatment 8 +/- 14 During leuprorelin acetate treatment the r-AFS stages changed as follows: [table; see text] Using the scoring system 85.2% of the patients improved. Relief of dysmenorrhoea could be achieved in 95.4%, relief of dyspareunia in 64% and of pelvic pain in 69.4% of patients. Baseline hormone levels dropped sharply during treatment. [table; see text] Androstenedione, testosterone, blood pressure, body weight, haematological parameters, liver enzymes, creatinine, electrolytes and HDL-/LDL-cholesterin remained more or less unchanged. Side effects being hot flushes, sweating, sleeplessness, headache, nausea, depression and vaginal dryness were due to estradiol deprivation. In 135 patients resumption of menstruation occurred in 95.6% within the first three months post-treatment. 23 patients of whom 21 were judged as infertile, became pregnant immediately after treatment was finished. The study results confirm the efficacy of leuprorelin acetate depot in the treatment of even advanced stages of endometriosis.