The presence of an altered endothelium-mediated flow-dependent dilatation (FDD) of peripheral conduit arteries in insulin-dependent diabetic patients without microangiopathy is still controversial. We studied 10 normotensive and non atherosclerotic insulin-dependent diabetic patients (D group) without complication (neuropathy, microalbuminuria or neuropathy) and 10 control subjects (C group) matched for age, sex and BMI. Radial artery diameter (RAD, echotracking) and flow (RAF, Doppler) were measured at baseline and during FDD in response to distal hand skin heating (from 34 to 44 degrees C). a method developed to increase RAF by stable steps by decreasing gradually hand skin vascular resistance. Endothelium-independent dilatation was evaluated by administration of glyceryl trinitrate (GTN: 0.3 mg spray). At baseline, there was no difference between group for RAF (C: 18 +/- 5 vs D: 18 +/- 2 mL/min; NS) and RAD (C: 2.51 +/- 0.12 vs D: 2.54 +/- 0.07 mm; NS). Heating induced in the diabetic group a smaller increase in RAF (C: 473 +/- 126% vs D: 262 +/- 63%; p<0.05) and RAD (C: 22.6 +/- 2.6% vs D: 16.1 +/- 1.8%; p<0.01). This last result remains significant when the increase in RAF was included into the analysis of RAD variation during heating (p<0.05). GTN-induced dilatation was similar in the 2 groups. Our results obtained by use of the hand skin heating method demonstrate the presence of an abnormal arteriolar skin reactivity and an altered peripheral conduit artery endothelium-dependent dilatation in uncomplicated insulin-dependent diabetic patients. The early identification of these anomalies, with negative prognostic value, could contribute to the management of these patients.