Fifty-one women with pelvic endometriosis were treated with the gonadotropin-releasing hormone agonist (GnRHa) Buserelin (Hoechst Holland N.V., Amsterdam, The Netherlands) 300 μg three times a day intranasally for 6 months. Forty-nine women completed treatment; 42 were available for 6 months of follow-up following treatment. Symptoms showed prompt and significant improvement. Follow-up after treatment revealed persistent relief from dysmenorrhea and dyspareunia in, respectively, 58.6% and 88.2% of the women, whereas pelvic pain returned to pretreatment scores. Serum estradiol (E2) was suppressed to predominantly early follicular phase concentrations. Laparoscopy at the end of therapy showed significant reduction of scores for implants only. There was no relation between the degree of E2suppression during therapy and the improvement of symptoms or the reduction of endometriosis. Statistical analysis in 22 infertile patients, of whom 7 conceived during follow-up, revealed no differences in E2levels during therapy, improvement of symptoms, or reduction of endometriosis. Buserelin appears to be safe, well tolerated, and effective in the management of endometriosis and associated complaints.