Five women with prior suboptimal ovarian stimulation for in vitro fertilization and embryo transfer (IVF-ET) were pretreated with a long-acting gonadotropin-releasing hormone (GnRH) agonist beginning in the midluteal phase of the preceding menstrual cycle. The four women with normal luteal function had castrate estrogen levels following regression of the corpus luteum, whereas one woman with an abnormal luteal phase and perimenopausal levels of gonadotropins had an agonistic response. In the three women with adequate stimulation, 20 oocytes were obtained and one women became pregnant. Initiation of GnRH agonist therapy during the luteal phase of a normal menstrual cycle may be an efficient way of obtaining ovarian suppression without an agonistic response.