In an attempt to define the role of autonomic neuropathy in the pathogenesis of diabetic foot ulcers, we have studied diabetic patients with and without ulcers, and a group of non-diabetic controls. A series of standard autonomic function tests have been compared with measurement of the Galvanic Skin Response (GSR). Patients with foot ulcers showed evidence of more severe somatic and autonomic neuropathy than diabetic subjects with no ulcer. The GSR was found to correlate well with the more conventional tests. In addition it proved to be abnormal more often than any other test for autonomic neuropathy in the diabetic patients with foot ulcers. In a preliminary follow-up study 2 patients with an abnormal GSR but no ulcer at the time of testing have subsequently acquired plantar ulcers. It is suggested that the GSR may prove to be a useful means of detecting diabetic patients at risk from foot ulceration.