The aims of this study were to assess autonomic nervous function in subjects with recently diagnosed Parkinson's disease (de novo patients) and to evaluate its changes following acute levodopa administration. In 13 patients (8 males, 5 females) and 13 age-matched control subjects, three cardiovascular autonomic function tests (Deep Breathing, Valsalva, Lying to Standing) were performed, the QT interval was calculated on a 12-lead electrocardiogram, and the response of plasma norepinephrine to standing was assessed in basal conditions. The cardiovascular tests and the measurement of the QT interval were repeated in de novo Parkinsonian patients 90 minutes after the administration of levodopa 200 mg per os. The results of the Deep Breathing and Valsalva tests were worse and the QT interval longer in patients than in control subjects (although the differences were not statistically significant). The heart rate increase at 30 seconds after standing up was significantly higher in Parkinsonian patients than in the control group. The response of plasma norepinephrine to standing was similar in both groups. Levodopa administration produced a slight improvement in the Deep Breathing test, a shortening of the QT interval and increased tachycardia on standing. Our data suggest that a mild subclinical impairment of parasympathetic function can be a feature of de novo Parkinsonian patients and that levodopa therapy could have a beneficial effect on this autonomic dysfunction.