The pituitary reserve of gonadotropins was evaluated with intravenous injections of 25 mug of synthetic luteinizing hormone-releasing hormone (LH-RH) in 32 patients with secondary amenorrhea. An obvious individual difference in the magnitude of the serum LH response was noted in these patients. Thus the patients were classified into four groups according to their pituitary responsiveness as expressed by the ratio of the serum LH stimulated peak to the basal level. Patients with values within the range of, or higher than, that of the normal follicular phase were classified as having high response (750% and above); within the range of that of the normal luteal phase as having moderate response (500 to 740%); between that of the normal luteal phase and that of postmenopausal women as having low response (250 to 490%); and within the range of, or lower than, that of postmenopausal women as having no response (240% and below). Among 26 clomiphene-failed patients in this series who were treated again with clomiphene and subsequent injection of LH-RH; 10 of 12 patients (25 or 35 cycles) with high response, 6 of 10 patients (12 of 28 cycles) with moderate response, and 1 of 4 patients (1 of 13 cycles) with low response ovulated. Five patients became pregnant. The results of this study indicate that in amenorrheic women the higher the pituitary response to LH-RH the greater the chance of inducing ovulation. Patients with secondary amenorrhea may thus be classified by assessing their pituitary response to LH-RH, which may be useful in predicting the chance for the successful induction of ovulation.