Disturbed hemodynamic reactions to insulin-induced hypoglycemia have been documented in diabetic patients and considered related to hyperinsulinemia and impairment of autonomic nervous functions. In the present study we investigated the effect on skin microcirculation of insulin-induced hypoglycemia obtained during moderate hyperinsulinemia, in 7 men with type 1 diabetes and in 8 healthy age- and sex-matched controls. The patients had all normal cardiovascular reflexes as assessed by respiratory sinus arrhythmia and Valsalva ratio. The skin microcirculation of the left fourth finger nailfold was investigated by laser Doppler fluxmetry, and the skin temperature within the same area was measured by a thermistor. Hypoglycemia was induced by a constant insulin infusion of Actrapid Human, 0.034 U kg-1 h-1 during 120 min. Plasma adrenaline, noradrenaline and pancreatic polypeptide increased significantly in both groups during hypoglycemia and the insulin levels never exceeded 50 mUl-1. A close to identical arterial hypoglycemia was obtained in the two groups 60 min after onset of insulin infusion. During hypoglycemia the control subjects revealed a significant decrease in laser Doppler flux (p < 0.025), while it was unchanged in the diabetic patients. Simultaneously, the skin temperature decreased (p < 0.05) in the controls, but was unchanged in the diabetic patients. The present study indicates that type 1 diabetic patients with normal cardiovascular reflexes have an abolished vasoconstrictor response in skin microcirculation of fingers during insulin-induced hypoglycemia, despite the fact that neurogenic and neuroglucopenic symptoms developed in these patients during hypoglycemia.