This study was conducted to evaluate sympathetic cardiac innervation using MIBG imaging in PD. Uptake of MIBG was measured in 35 PD patients. Although normal MIBG uptake was observed in PD patients with HY stage l, PD with stage 3-5 revealed a total defect of visual MIBG imaging on heart area. Quantitative measurements of MIBG uptake assessed by the radioactivity ratio of cardiac to mediastinal tissue(H/ M) in early imaging was associated with the clinical severity of PD(control; 2.0 +/- 0.3, stage l; 2.0 +/- 0.1, stage 2; 1.6 +/- 0.4, stage 3-5; 1.3 +/- 0.1). In conclusion, homogeneous impairment of sympathetic cardiac innervation was observed in PD patients and this abnormality was associated with the clinical severity of PD, indicating that MIBG imaging of heart is useful not only for the evaluation of cardiac sympathetic impairment of PD but also for the diagnosis of PD.