The pulsatile pattern of gonadotropin secretion regulates follicular growth and corpus luteum function in normal cycles, but the role of endogenous gonadotropin pulses in hyperstimulated cycles is unclear. We studied pulsatility of serum-luteinizing hormone (LH) in the late follicular and midluteal phases in four women after hyperstimulation with clomiphene citrate, human menopausal gonadotropin, and human chorionic gonadotropin, and in five women with normal untreated cycles. In the late follicular phase, the number, interval, amplitude, and area of LH pulses did not show significant differences between hyperstimulated and control cycles. In the midluteal phase, the long-lasting (greater than 90 minutes) LH pulses typical for the normal luteal phase, were not found after hyperstimulation. As the length of the luteal phase in these cases was normal, the significance of this finding remained obscure.