During the past decade, the development of various gonadotrophin-releasing hormone (Gn-RH) agonists, which induce reversible hypo-oestrogenism has opened a new area in the medical management of endometriosis. In an open, multicentre phase III study, the efficacy, tolerance and safety of the Gn-RH agonist leuprorelin acetate were tested. The preliminary results of 104 women treated in seven German centres are presented. Pelvic endometriosis was diagnosed by laparoscopy and classified according to the American Fertility Society scoring system: 33% of patients had minimal, 22% mild, 28% moderate and 8% severe endometriosis and in 9% no pathological results were obtained. The patients' mean age was 30 +/- 6 years and 66 had infertility problems. Treatment was started within the first 3 days of the menstrual cycle and consisted of a subcutaneous injection of leuprorelin acetate 3.75 mg, repeated once monthly over 24 weeks. A follow-up period of 12 months after the last injection has been completed in 70 patients, including a second laparoscopy. At all visits, symptoms were evaluated, physical examinations performed, and blood samples collected for haematological screening, serum chemistry determinations and measurement of the gonadotrophins oestradiol and progesterone and leuprorelin acetate. The median score at laparoscopy fell from 12 before operation to 8 after operation and 2 after treatment with leuprorelin acetate. Of the total number of patients, 89% had improvements in their endometriosis, 8% a deterioration and 3% no change. Patients reported improvement in the following: dysmenorrhoea 93%, dyspareunia 62% and pelvic pain 70%. However, all women complained of at least one of the following symptoms: hot flushes 86%, sleep disturbance 62%, sweating 61%, headache 41%, nausea 32% and depression 20%. Fifty-five percent of patients reported additional side effects such as vaginal dryness, fatigue and lower abdominal pain. After the third injection, amenorrhoea persisted in 94% of the women. Four weeks after the first leuprorelin acetate injection median concentrations of oestradiol fell from 45 pg/ml to 11 pg/ml, follicle-stimulating hormone from 7 U/L to 3 U/L and luteinising hormone from 5 U/L to 1 U/L and remained almost unchanged over the observation period. During the 6 months' treatment, laboratory parameters showed no significant deviations from normal; only total cholesterol, high-density lipoprotein cholesterol and alkaline phosphatase increased. Treatment results were judged as good and satisfactory in 82% and 11% of cases, respectively. On the basis of this study, it can be concluded that leuprorelin acetate treatment is safe, well tolerated and effective in the medical management of endometriosis and endometriosis-related complaints.