Despite the well established negative relationship between adiposity and GH secretion, the effect of adolescent obesity on plasma IGF-1 and insulin regulation of IGF binding protein-1 (IGFBP-1) levels has not been established. To examine this issue we studied 13 obese adolescents (14.6±1 yrs; BMI34±3); 16 lean adolescents (14±1 yrs, BMI 23±1) and 9 lean adults (23±1 yrs, BMI 22±1), during a two step 8 and 40 mU/m2.min euglycemic clamp and a hyperglycemic clamp (+125 mg/dl). Fasting plasma insulin levels were significantly greater in obese adolescents compared with both lean groups, whereas, basal plasma IGF-1 levels were lower in obese than in lean adoelscents (348±41 vs 546±38 ng/mL, p<0.02). Basal IGFBP-1 levels were markedly reduced in obese adolescents(17±4 ng/mL) versus lean adolescent (39±6 ng/mL; p<0.01) and lean adults 60±6 ng/mL; p<0.001) and fasting IGFBP-1 concentrations were inversely related to basal plasma insulin levels in all 3 groups(p<0.03). Of interest, insulin induced suppression of IGFBP-1 levels were reduced in the obese group compared woth both lean groups during the low and high insulin dose clamp, and during the hyperglycemix clamp. These data indicate that in obese adolescents; 1) IGF-1 and IGFBP-1 levels are low and 2) Raising plasma insulin above fasting levels has little further effect on already suppressed plasma IGFBP-1 levels. Chronically depressed levels if IGFBP-1 in adolescent obesity may serve to increase the bioavailability of IGF-1 which may in turn contribute to lower ciurcultaing GH and total IGF-1 concentrations.