Thirty-six women with histories of regular cycles undergoing elective laparoscopic sterilization volunteered to participate in a research program of endometrial biopsy, oocyte donation, and in vitro fertilization (IVF). One half of the volunteers received 5 days of 150 mg of clomiphene citrate (CC) ending 5 days before human chorionic gonadotropin injection and 6.5 days before laparoscopy and biopsy. The control patients were treated identically, except they received no CC. CC cycles were more uniform in duration and follicular response better, enabling a prescheduled IVF regimen. Control cycles were complicated by poor follicular response or untimely endogenous surges of luteinizing hormone (LH). The mean urinary estrone glucuronide excretion per follicle was the same in each group, and there was no evidence of a luteal defect by either luteal phase length or urinary pregnanediol excretion. Although there were minor differences in mitotic rate and basal vacuolation of glandular epithelium in biopsies, no specific deleterious effect of CC could be seen.