Sympathetic nerve function was studied by the Silastic mold technique and by evaporimetry in the hand and the foot in 357 type I diabetic patients. The number of active sweat glands was below normal in 24% of patients in the hand and in 56% in the foot, while the sweat evaporation rate was low in 17% and 40% of patients, respectively. Computerized analysis of the molds, which allowed automatic sweat gland counts and estimations of the secretion volume of each sweat gland, detected abnormalities in 36% and 60% of patients. The Silastic imprint technique was found to be a sensitive test for detection of sympathetic nerve involvement, even in asymptomatic patients with normal clinical and nerve conduction examinations. Its sensitivity and accuracy has been enhanced by the computerized analysis of the molds.