At the turn of the century, reports on a coincidence of pineal tumors and precocious puberty in man initiated a host of animal experiments. Results of these experiments ultimately revealed a modulating effect on sexual maturation and on gonadal activity in several species, brought about by the pineal hormone melatonin (aMT) and particularly its circadian secretion pattern. In addition, it renewed interest in a possible interaction of the pineal and human sexual function. The introduction of specific and precise aMT assays provided exact evaluation of the circadian aMT secretion pattern in adults. Despite considerable efforts, however, a precise characterisation of this pattern has not yet been achieved in children. In a first step we examined single day- and nighttime serum samples from 280 subjects of all ages. aMT levels were low during early infancy, increased to their highest values around 1 to 3 years and dropped progressively by 75 percent until young adulthood, when they remained fairly stable. Thus, the pattern of aMT levels is the reverse of that of gonadotropin levels or gonadal activity in humans. Whether there is a causal relationship between the activity of the pineal gland and the hypothalamo-pituitary-gonadal axis in humans or whether the described negative correlation in the activity of both glands is purely coincidental remains to be clarified.