alpha-Subunit and gonadotropin responses to a LHRH infusion (0.2 micrograms/min) for 4 h were studied in eight hyperprolactinemic amenorrheic women, ages 23-40, and in five normal women in the early follicular phase of the menstrual cycle. Basal alpha-subunit and LH concentrations were comparable to normal women; however, basal FSH concentrations were significantly (P less than 0.05) lower. Peak serum alpha, LH, and FSH concentrations during the LHRH infusion were significantly higher than controls (P less than 0.01, P less than 0.05, and P less than 0.01, respectively). Gel chromatography of serum confirmed the presence of both free alpha-subunit and intact LH which had normal biological activity. Six of the women were restudied in the early follicular phase of the cycle after return of normal ovulatory function and normalization of serum PRL concentrations. During bromocriptine therapy, peak serum alpha, LH, and FSH concentrations decreased significantly (P less than 0.02, P less than 0.05, and P less than 0.001, respectively) and were comparable to control subjects. The changes in serum alpha and gonadotropin responses to the LHRH infusion during bromocriptine therapy occurred independently of the serum estradiol concentrations. Abnormalities in the regulation of alpha-subunit and gonadotropin secretion are present in hyperprolactinemia. These abnormalities reverse with bromocriptine therapy and may occur independently of changes in gonadal steroids.