To clarify the factors affecting pituitary prolactin (PRL) reserve during development, the serum PRL response to TRH and serum LH, FSH response to LH-RH were studied. The basal levels of serum estradiol (E(2)), testosterone (T) and dehydroepiandrosterone-sulfate (DHEA-S) were measured in 128 normal children and adolescents and 18 cases of Turner's syndrome. In males, no correlation was found between E(2), T, DHEA-S and the integrated secretion of PRL (∑PRL), while a positive correlation was found between the integrated secretion of FSH (∑FSH) and ∑PRL (p<0.05). In females, positive correlations were found between E(2) and ∑PRL (p<0.01), the integrated secretion of LH (∑LH) and ∑PRL (p<0.01) and DHEA-S and ∑PRL (p<0.01). E(2) was selected as the explanatory variable of ∑PRL by means of multiple regression analysis. In cases of Turner's syndrome, endocrinologically characterized by high gonadotropins and low E(2), a positive correlation was found between ∑FSH and ∑PRL (p<0.05). These findings suggest a stimulating effect of E(2) on PRL reserve in females and the stimulating effect of endogenous LH-RH on PRL reserve in both sexes in children and adolescents.