Plasma levels of gonadotropins, PRL, T4, and adrenal and gonadal steroids were measured in two groups of 7- to 9-yr-old and 10- to 11-yr-old obese prepubertal girls, and were compared to those found in groups of nonobese girls of the same age. The data found in normal weight subjects confirm the data reported in the literature, showing a significant rise between the 7- to 9- and 10- to 11-yr groups, of FSH, pregnenolone, dehydroepiandrosterone, testosterone, and estradiol plasma levels, while LH, PRL, T4, cortisol, progesterone, 17-hydroxyprogesterone (17P), and androstenedione remained constant. In the obese subjects, pregnenolone and dehydroepiandrosterone levels are notably higher than in the normal girls, in the same range as those found in adult women; furthermore, they show no rise between the two age groups. The obese prepubertal groups had significantly higher progesterone, androstenedione, and PRL levels in comparison with those observed in girls of normal weight, but 17-hydroxyprogesterone, cortisol, testosterone, LH, and T4 were similar in both groups. Estradiol levels were markedly depressed in the obese girls; FSH levels were higher in the younger girls than in normal subjects. These data indicate that in prepubertal obesity, maturation of adrenal gland function (chiefly the delta 5 pathway), is notably enhanced, whereas gonadal secretion of estradiol is impaired in the presence of high levels of FSH and PRL.