OBJECTIVE To determine the safety and effectiveness of ZOLADEX depot (goserelin) in the therapy of endometriosis (study No. 9393CZ/0001). METHODS A multicentric prospective open study of 60 women with endometriosis. R-AFS score of pelvic endomemtriosis was established in patients suffering from pelvalgia, dyspareunia and dysmenorrhoea during pre-treatment laparoscopy. The effect of Zoladex depot applied subcutaneously were evaluated by gynaecological and laboratory examinations, including assessment of subjective complaints every four weeks in the course of six months. Laparoscopic check-up was carried out immediately after terminating the therapy. RESULTS (1) The average total score of subjective complaints decreased by 90% after 24 weeks of treatment. (2) Treatment was successful in 67% patients, i.e. laparoscopic examination showed a decrease of the R-AFS score by at least 50%. In 28% treated women visible endometrial foci disappeared completely. (3) The most frequent side-effects of therapy are associated with hypoestrogenic effects of GnRH agonists. Vasomotor instability, flushes and night hyperidrosis occurred in 93% and 90% treated women, respectively. CONCLUSIONS Goserelin acetate is a synthetic GnRH agonist suitable for safe and effective therapy of pelvic endometriosis. The administration of 3.6 mg goserelin every day for 24 weeks reduced markedly the size of endomerial foci and painful symptoms.