Sudomotor function in 83 patients with Parkinson's disease (PD) was evaluated using the sympathetic skin response (SSR) and sweat response to intradermal acetylcholine (ACh) injection. The incidence of abnormal SSRs (36.1%) increased, and the size of the response decrease with the severity of the illness. Neither the incidence of abnormal SSRs nor the amplitudes of the responses were influenced by levodopa or an anticholinergic agent. The SSR therefore can be used to evaluate the sudomotor efferent pathway in PD patients. In all the patients who had no SSR response, the local sweat response to ACh showed a reduced number of excitable sweat glands and low sweat volume. One patient, whose local sweat response to ACh was markedly impaired, had unmyelinated and acetylcholinesterase-positive fiber densities that were in the normal range in his biopsied sural nerve. The abnormal sweat response to ACh is considered to reflect the dysfunction of postganglionic sympathetic fibers in PD patients.