Four normal pubertal boys had plasma LH and melatonin measured at 20-minute intervals for 24-hours. All four subjects showed a significant augmentation of LH and melatonin during nocturnal sleep. There was also a significant correlation between the LH and melatonin levels (P less than 0.001). These data indicate that the peripheral concentrations of melatonin which occur during sleep are insufficient to prevent spontaneous LH secretion during puberty.