We report -108Met/Val polymorphism of the COMT gene in Japanese patients with Parkinson's disease (PD). The allele frequency for -108Val was higher in PD patients compared with controls, although the differences did not reach the statistical significance. However, the frequency of -108Val homozygotes was significantly higher in PD patients (56.8%) than in control subjects (44.2%), and heterozygotes of -108Met/Val were less in PD. COMT gene polymorphism may constitute a genetic risk factor for PD among Japanese.