ABSTRACT.Recently we reported that insulin resistance and glucose induced insulin release are inversely correlated to age in young healthy siblings of diabetic patients. To confirm this pattern of change with age, the subjects were reexamined after two years. The study was limited to the age groups with the lowest insulin sensitivity, i. e. 14.0‐15.9 years for females and 16.0‐17.9 years for males. All five girls and four of five boys showed an increased insulin sensitivity as measured by the somatostatin‐insulin‐glucose infusion test (p=0.02). All subjects showed a decrease in fasting levels of insulin‐like growth factor 1 (IGF‐1) (p<0.01) during the observation period. All except one showed an increase in the levels of dehydroepiandrosterone sulphate (DHEA‐S) (p<0.01). These data confirm that insulin sensitivity increases in the late teenage period. The parallelism to the changes of IGF‐1 indicate that the pubertal changes in insulin sensitivity may partly be caused by growth hormone. Our data contradict the hypothesis that the low insulin sensitivity of puberty is due to the increased l