BACKGROUND: The study of sudomotor function represents a useful tool to evaluate autonomic disorders. Currently available tests allow either the measurement of sweat output from the whole body or selected small skin locations over time, or quantification of the number and size of sweat drops at a fixed time after stimulation. We devised a dynamic sweat test (DST) that measures at the same time sweat gland density, distribution of active glands, and sweat rate, and applied it to the evaluation of sudomotor function in diabetes. METHODS: The DST was used to evaluate sweating in the forearm of 14 asymptomatic diabetic subjects and 14 age-and sex-matched healthy controls. Distal leg was also tested in 7 patients and 7 controls. The formation of the imprint of pilocarpine-induced sweating was recorded by a digital video camera through a cornstarch-powdered transparent tape used as a contrast-enhancing device. Mean sweat output per gland and per skin area and sweat gland density per cm were evaluated. RESULTS: We observed a significant reduction of sweating in diabetic subjects as compared to controls; sweat gland density per cm (59.7 ± 18.6 vs 83.7 ± 17.3; p < 0.05) and mean sweat output (nL/min) per gland (4.7 ± 0.7 vs 8.3 ± 2.7; p = 0.01) and per skin area (261 ± 100 vs 645 ± 296; p = 0.01) were reduced in the lower limb. Values for the forearm were not significantly different from controls. CONCLUSIONS: Dynamic sweat test is an easy-to-perform, informative method to study sudomotor function. It provides the ability to detect subtle functional changes occurring in the early stages of diabetic neuropathy.