Three different stimulation protocols were tested in patients affected by stage I and II endometriosis with no other causes of infertility, and scheduled for the gamete intrafallopian transfer technique. In two protocols a gonadotropin hormone-releasing hormone analog was used. The analog was started 6 months before stimulation in the former and along with the exogenous gonadotropin in the latter. Patients receiving only gonadotropin served as controls. Sixty patients were selected for this study; 55 reached laparoscopy. Whereas patients receiving either gonadotropin alone or simultaneous analog and gonadotropin had similar pregnancy rates, this was much higher in the patients undergoing a prolonged, medically induced hypoestrogenism. Prolonged analog pretreatment before ovarian stimulation may give better chances of success in endometriosis patients undergoing assisted reproduction techniques.