Several tests of cardiovascular and gastrointestinal function have been approved for the diagnosis of autonomic regulation dysfunction in Parkinson's disease. In the present study we compared the diagnostic value of the sympathetic skin response (SSR) with the established methods. Ninety percent of the 20 patients we examined (10 women, 10 men, 46 to 80 years) showed pathological results in the cardiovascular function test. Fifty-five percent had a prolonged colon transit, indicating a gastrointestinal dysfunction. We saw pathologically prolonged latencies of the SSR in 35% of the patients, 55% had borderline results. Three of the 20 patients had pathological results in all of the functions examined. Half of the patients had two pathological results, whereas 7 patients were pathological in only one of the three examinations. We were unable to establish any correlation between the SSR and other results, and we also found no relationship between prolonged SSR and the duration of the disease.