Studies on the relation between the pineal and human puberty have yielded conflicting results, partly due to methodologic issues, such as failure to consider the characteristic secretory rhythm of melatonin, or exclusion of normal subjects. Melatonin nocturnal rhythm was assessed in 62 normal subjects (ages 5–17 years), in whom hourly blood samples were collected by constant withdrawal from 18.00 to 08.00 h. Melatonin peak and mean integrated nocturnal concentrations were highly correlated (r = 0.90, p