Fifty-two long-term diabetic patients without symptoms of autonomic neuropathy and 31 age-matched healthy controls were tested for autonomic neuropathy by deep breathing, Valsalva maneuver, and an orthostatic test on tilt table. The deep breathing and the orthostatic tests showed significant parasympathetic impairments in patients with signs of peripheral neuropathy. The Valsalva maneuver, which also mainly reflects parasympathetic: function, was disturbed in patients with peripheral neuropathy, but only in those with a very long duration of diabetes. Parasympathetic neuropathy was closely correlated with peripheral neuropathy. However, five patients showed signs of parasympathetic neuropathy but not of peripheral neuropathy. Thus, parasympathetic neuropathy can appear before peripheral neuropathy. On the contrary, sympathetic denervation, as shown from the blood pressure reaction to tilting, only appeared in patients with peripheral neuropathy.