Plasma free dehydroepiandrosterone (DHA), androstenedione (Δ), testosterone (T), dihydrotestosterone (DHT), estrone (E1), and estradiol (E2) were measured by radioimmunoassay in 55 boys and 54 girls 3.5 to 16.3 years of age. Plasma DHA increased significantly between 6 and 8 years of age in girls and between 8 and 10 years of age in boys. A further significant increase was noted between 10 and 12 years of age in both sexes. Δ rose significantly between 8 and 10 years of age in girls and between 10 and 12 years in boys. In contrast, no significant increase in T, DHT, or E1, was noted prior to 12 years of age in both sexes. However, E2 showed a significant increase between 10 and 12 years of age in girls. This early rise in the course of pubertal development of the two sex steroids predominantly of adrenal origin, DHA and Δ, and its occurrence 1 to 2 years earlier in girls than in boys, as does puberty itself, suggest a possible role for these steroids in the mechanisms involved in triggering the hypothalamic-pituitary-gonadal axis at puberty.