In 104 normal boys, aged 7 to 14 years (bone ages 5 to 15 years), plasma dehydroepiandrosterone (DHEA) rose from 52.7 at 7 years, to 112.0 ng/100 ml at 10 years. A further rise occurred at 12 years (188 ng/100 ml). In relation to the bone age, DHEA increased from a mean plasma level of 31.1 at a bone age of 5 years to 77.1 ng/100 ml at one of 7 years. Further increases were observed with mean values of 163.2 at a bone age of 11 years, and of 221.2 at a bone age of 12 years, with a maximum of 333.4 ng/100 ml at bone ages of 14-15 years. The first significant increase of plasma testosterone (T) was noted at a bone age of 12 years (54.8 ng/100 ml). The major rise of T was preceded by the rise of plasma LH and was accompanied by the rise of plasma FSH. Plasma DHEA and T were also measured in 123 normal girls, ages 6 to 13 years (bone ages 5 to 15 years). DHEA rose significantly from a mean level of 44.7 at 6 years, to 80.9 ng/100 ml at 8 years, with further increases between 9 and 10 years and between 10 and 11 years. In relation to bone age, DHEA increased significantly from a mean plasma concentration of 30.9 at a bone age of 5 years, to that of 58.6 ng/100 ml at 7 years. Further increases were observed with values of 191.1 at a bone age of 10 years and 485.6 ng/100 ml at a bone age of 13 years. The first significant rise of testosterone (T) occurred at 10 years of both chronological and bone age. DHEA rose before the increase of gonadotropins. The major rise of T at a bone age of 10 years occurred concurrently with increases in plasma FSH and LH. Low levels of DHEA were observed in Addison's disease. In hypogonadotropin hypogonadism and in anorchia, DHEA levels were normal, suggesting that DHEA is produced primarily in the adrenal gland. In seven girls with early adrenarche, plasma concentrations of DHEA were in the upper range of normal values, whereas T levels were within the normal range. Conversely in girls with late adrenarche, plasms DHEA was lower than normal but T was within the normal limits. The elevation of DHEA prior to the first signs of puberty suggests that DHEA may play a role in the maturation of the hypothalamic-hypophysealgonadal axis. However, the mechanism that triggers the secretion of DHEA is not known.