Plasma and urinary melatonin in male infants during the first 12 months of life.

Plasma and urinary melatonin, testosterone and luteinizing hormones were radioimmunologically assayed in 26 male babies during the first year of life. The results show that plasma melatonin levels are low during the phase of postnatal elevation of testosterone and luteinizing hormones. They subsequently increase when testicular activity decreases. Urinary elimination of melatonin does not vary during this period, suggesting the existence of variations in the synthesis or utilization of melatonin.