SUMMARYThe peripheral venous plasma concentrations of gonadotrophins (LH and FSH), prolactin (Prl), cortisol, dehydroepiandrosterone (DHA), dehydroepiandrosterone‐sulphate (DHA‐S), pregnenolone (Δ5P), progesterone (P), 17‐hydroxyprogesterone (17P), androstenedione (A), testosterone (T), dihydrotestosterone (DHT) and oestradiol (E2) were measured in girls at different stages of sexual development (from P1 to P4–5 according to Tanner, 1962). Both gonadotrophins increase progressively during sexual maturation, to reach the highest concentrations in P4–5. However, the FSH values were significantly lower in these P4–5 pre‐menarchal girls than those found in adult women in the early follicular phase. No significant changes were found in plasma Prl, cortisol and 17P levels during pubertal development; in contrast, plasma concentrations of DHA tripled from P1 to P4–5, reaching adult levels. A progressive rise was also found in DHA‐S plasma levels. A significant, but less evident increase was found in Δ5P and P plasma concentrations, from group P1 to P4–5. A, T and DHT levels rose progressively and significantly from P1–2 to the end of sexual maturation. In the case of E2, only a moderate increase was found during pubertal development.All these data indicate that during pubertal development, there is a progressive reduction in the sensitivity towards oestrogen of the hypothalamic centres controlling gonadotrophin secretion.Prl does not seem to be involved in human sexual maturation, while important changes have been found in adrenal androgens. The constant levels of 17P and cortisol, in comparison with the behaviour of DHA, DHA‐S, T and A, seem to indicate that during this period of life, the adrenal gland is stimulated by unknown factors other than ACTH, acting on the adrenal androgen‐producing cells and responsible for the reported rises