Synthetic luteinizing hormone releasing hormone (LHRH), 100 µg, was administered intravenously to 29 normal individuals. In male subjects, both baseline and peak LH reponse values showed minimal variations between subjects. The FSH baseline and response were more variable. In normal females the FSH and LH baseline values and response to LHRH infusion showed greater variation than that seen in male subjects, and this variation correlated with the phase of the menstrual cycle. In perimenopausal women with elevated baseline gonadotropins, the absolute LH peak values were comparable to those seen during the periovulatory period of the menstrual cycle, while FSH baseline and peak values were unmistakably higher than those observed in the normally menstruating women. Three women under gonadotropic suppression by three different drugs were investigated; megestrol suppressed the LHRH response more effectively than either diethylstilbestrol or an oral contraceptive. The LHRH stimulation test reflects only the ability of the pituitary cell to release gonadotropins. In a normal individual, however, some justifiable assumptions can be made regarding the immediate past synthesis and release versus accumulation of pituitary LH.