We evaluated the cardiac innervation status of patients with idiopathic Parkinson's disease (IPD), in order to recognize cardiac dysautonomia at an early clinical stage, using I- -iodobenzylguanidine ( I-MIBG) scintigraphy and its relation to other clinical and laboratory parameters. Fourteen patients with IPD at Hoehn-Yahr stage I and 11 age-matched controls were studied. Patients were scored according to the Unified Parkinson's Disease Rating Scale (UPDRS) in aspects of daily life activities, cognitive and emotional status and motor examination. All patients underwent 5 min electrocardiographic recordings in order to assess the heart rate variability. Planar I-MIBG studies at 15 min and 3 h after intravenous injection of 185 MBq were performed. Heart-to-mediastinum (H/M) ratios were calculated. Plasma catecholamine levels were also evaluated. The mean H/M ratios in patients and controls were 1.84+/-0.40 and 2.35+/-0.29, respectively (P <0.05). Although the mean plasma adrenaline and noradrenaline levels were in the normal range, a weak inverse correlation existed between the noradrenaline levels and late I-MIBG H/M ratios (r =-0.442), which was not statistically significant. There were no correlations between the other parameters. Eight patients had normal electrocardiography, whereas four had findings of autonomic imbalance. In conclusion, cardiac dysautonomia is common and seems to occur independent of the clinical stage and symptoms in patients with IPD. I-MIBG scintigraphy is a powerful tool in its assessment.