This study was undertaken to examine whether insulin resistance in adolescents with poorly controlled type 1 diabetes mellitus (T1DM) is associated with the failure of insulin to suppress lipolysis in adipose and muscle tissues. Using microdialysis techniques, extracellular fluid concentrations of glycerol was measured in adipose and muscle tissue 3 h before and 3 h during a 0.8 mU x kg-1 x min-1. euglycemic clamp. Ten adolescents with poorly controlled T1DM (HbA1c 10.2 +/- 0.2%) were compared with six healthy lean adolescent control subjects. Despite similar increases in plasma insulin in both groups, diabetic subjects exhibited a 39% reduction in peripheral glucose uptake compared with controls (p < 0.05). In contrast, hepatic glucose production was fully suppressed by insulin in diabetic subjects. At the end of the clamp, extracellular glycerol concentrations were significantly elevated in subjects with diabetes (muscle: 85 +/- 7 microM for diabetics and 51 +/- 8 microM for controls, p < 0.01; adipose: 149 +/- 23 microM for T1DM and 82 +/- 11 microM for controls, p < 0.05), indicating impaired in situ suppression of lipolysis in patients with diabetes. With all subjects considered, the rate of insulin-stimulated metabolism was inversely correlated to glycerol concentration in both adipose (r = -0.63, p < 0.01) and muscle (r = -0.63, p < 0.01). Our data suggest that failure of insulin to inhibit lipolysis in muscle and adipose tissue contributes to the severe peripheral insulin resistance that characterizes poorly controlled T1DM during adolescence.