Eighty-seven patients undergoing in vitro fertilization were studied to evaluate the prognostic value of different tests in predicting ovarian stimulation response. We studied basal follicle-stimulating hormone (FSH) value on cycle day 3, the clomiphene citrate (CC) challenge test and serum estradiol levels on cycle day 3. Patients with elevated basal FSH levels needed more ampoules of gonadotropins for stimulation and had a higher cancellation rate because of poor response. Patients with abnormal CC challenge test results also needed more ampoules of gonadotropins, but the higher cancellation rate in this group did not reach statistical significance. The basal estradiol level did not contribute to further discrimination between groups. We conclude that basal FSH level on cycle day 3 is a useful prognosticator of ovarian stimulation response.