Gut dysmotility may result from disease of the extrinsic neural pathways supplying the gut. We report the results of studies on sweating, cardiovascular, and sudomotor reflexes in eight prospectively evaluated patients with apparently functional gastrointestinal disorders. There was no personal or family history of neurologic disease, except for one patient with known atony of the bladder. Motility of the esophagus, stomach, and small intestine were, respectively, abnormal in two, six, and seven patients and showed either uncoordination of contractions between segments or postcibal hypomotility. All had generalized or patchy anhidrosis; quantitative sudomotor axon reflex tests were also abnormal in four patients and borderline in one. Plasma levels of catecholamines were abnormal in one patient. All patients had evidence of sympathetic denervation: preganglionic in two patients, postganglionic in five patients, and mixed in one patient. Three patients also had abnormal heart-rate responses to deep breathing, suggesting parasympathetic dysfunction. No underlying cause for the autonomic dysfunction was identified in any of these patients despite extensive investigations. Thus, these data support the hypothesis that apparently functional gastrointestinal disorders may be due to idiopathic autonomic denervation.