It has been reported that the F-Dopa (FD) uptake in patients with idiopathic Parkinson's disease (PD) decreased significantly in the caudate and putamen when compared to controls. The FD uptake severely decreased in the putamen, while it was relatively spared in the caudate nucleus. We also previously reported that atypical parkinsonism with no or little tremor showed a homogeneously reduced FD uptake in both the caudate and the putamen. In this study we evaluated the caudate and the putaminal FD uptakes in relation to the three main symptoms in PD. The FD uptake was measured by PET with 6-L-[18F]fluorodopa in 17 patients with PD. The caudate and the putaminal FD uptake ratios to the cerebellum at 120 min were evaluated. The caudate and the putaminal FD uptake ratios in the patients with PD decreased as their clinical stages advanced. These decreases also correlated with the degree of rigidity and bradykinesia. However, such decreases did not correlate with the degree of tremor. The caudate-putamen index (CPI)(%), which was calculated by a formula based on the difference in the uptakes of the caudate and putamen divided by the caudate uptake, indicated 11.6 +/- 3.6, 16.5 +/- 5.5 and 18.3 +/- 4.1 in the group of no, mild and moderate tremor, respectively, and increased as the degree of tremor advanced. The CPI in the group of moderate tremor significantly increased from that in the group of no tremor (P < 0.04). However, the CPI did not correlate with the clinical stage, the degree of rigidity or the degree of bradykinesia. The FD/PET study therefore effectively demonstrated the severity of the clinical symptoms of rigidity and bradykinesia in patients with PD in correlation with a decrease in the FD uptakes in the caudate and the putamen, and it also demonstrated that the severity of tremor might have a different mechanism from that of such other symptoms as rigidity and bradykinesia.