Abnormalities of microvascular function may be important in the pathogenesis of diabetic microangiopathy. As such changes are already present at diagnosis in patients with Type 2 (non-insulin-dependent) diabetes mellitus, subjects at risk of developing the disease, who had elevated fasting plasma glucose concentrations below the diabetic range, were studied. The maximal microvascular hyperaemic response to local heating was determined in the feet of 11 subjects with fasting hyperglycaemia and 11 age- and sex-matched control subjects. There was reduced maximal hyperaemia in the subjects with fasting hyperglycaemia (1.01 [0.71-1.57]V, median and range), when compared to control subjects (1.41 [1.32-2.13]V, p < 0.001). It is unlikely that this limited vasodilation is a result of the mild degree of hyperglycaemia observed in the subjects included in this study. Further studies are therefore required to address the possible mechanisms of limited microvascular reactivity in subjects at risk of developing Type 2 diabetes.