Using a simple and standardized method we estimated both insulin secretion and insulin sensitivity in peripheral tissues in relation to Tanner pubertal stages. Early insulin response, mean blood glucose (MBG), mean serum insulin (MSI), glucose uptake rate in peripheral tissues and insulin sensitivity index (SI) in response to the standard oral glucose tolerance test were evaluated in 73 normal girls. Study subjects were divided into 4 groups: group 1 (Tanner stage I, n = 20); group 2 (Tanner stage II, n = 14); group 3 (Tanner stages III and IV, n = 15), and group 4 (Tanner stage V, n = 24). Steroid levels and insulin-like growth factors were determined to characterize clinical pubertal development. MBG was similar in all groups but MSI increased at stage II and retained similar values throughout puberty, with those of group I being statistically lower than in the other groups (p < 0.001). When MSI values were adjusted per kilogram of body weight, a significant increase was observed in group II (p < 0.05). The MSI adjusted values were: group 1, 1.0 +/- 0.4; group 2, 1.4 +/- 0.4; group 3, 1.0 +/- 0.3, and group 4, 1.0 +/- 0.4 mU/l/kg. SI values were similar in groups 1 and 2 and significantly lower than in groups 3 and 4 (p < 0.001). Our results confirm both that insulin secretion is related to age and that an insulin-resistant state occurs during puberty. Thus, the insulin-resistant state coincides with Tanner stage II. In conclusion, this mathematical approach is considered to be a simple and reliable method for analyzing the possible alterations in insulin secretion and action in children and adolescents in whom more sophisticated procedures must be limited in this early period of life for ethical reasons.