Twenty-three patients with Gilles de la Tourette's syndrome (GTS) underwent noninvasive investigation of autonomic nervous system (ANS) function, as did 23 age-matched controls. ANS function in GTS patients was no different from that of controls, and patients receiving neuroleptic drugs had the same ANS function as untreated patients. All 23 patients later received clonidine and were retested. The ANS values before administration of clonidine were compared with those while patients were taking clonidine. The only significant change (p less than 0.01) with clonidine was a reduced resting pulse rate. The combination of clonidine and neuroleptic drugs did not induce significant autonomic changes compared with neuroleptic therapy alone. These results indicate that the ANS in GTS patients is normal and that the drugs used to abate tics do not produce clinically significant changes in ANS when chronically given. The findings suggest that the pathophysiology and treatment of GTS do not directly involve the nuclei or tracts of autonomic regulation.