We investigated the Gln --> Arg 191 polymorphism-in paraoxonase (PON1) in St. Petersburg population, in three clinically differentiated groups of patients with Parkinson's disease (PD) and in the symptomatic tremor group. A new approach for Gln --> Arg 191 PON1 polymorphism genotyping is suggested. No significant differences in the groups studies as compared to the controls was observed.