Peripheral autonomic neuropathy in diabetes has been difficult to evaluate. We have developed a test to quantitate sympathetic skin vasomotor function in the extremities. Skin vasomotor reflexes were investigated after warming and cooling the left arm and recording changes in skin temperature as a measure of skin blood flow in the right hand and both feet. Twenty-three diabetic patients with cardiac autonomic neuropathy and 28 healthy control subjects were examined. In contrast to the healthy subjects, the diabetic patients showed reduced or even absent responses in skin temperature to both warming and cooling. The rate of skin temperature decrease for the hand and feet during cooling, which was used as the actual parameter to quantitate skin vasomotor control, was significantly reduced in the diabetic group as compared with the healthy control subjects. We conclude that this technique provides a simple non-invasive method for quantitating skin vasomotor function in the extremities of diabetic patients.