Increased oxidative stress contributes to neuronal dysfunction in Parkinson's disease (PD). We investigated whether the pathological changes in PD brains may also be present in peripheral tissues. Leukocyte 8-hydroxydeoxyguanosine (8-OHdG), plasma malondialdehyde (MDA), erythrocyte glutathione peroxidase (GPx) and plasma vitamin E (Vit E) were measured for 211 PD patients and 135 healthy controls. Leukocyte 8-OHdG and plasma MDA were elevated, whereas erythrocyte GPx and plasma Vit E were reduced in PD patients when compared to the controls. After adjusting for environmental factors, logistic regression analysis showed that PD severity was independently correlated with 8-OHdG and MDA level, and inversely correlated with GPx activity and Vit E level. Leucocyte 8-OHdG level was continuously increased with advanced PD Hoehn-Yahr stages, while plasma MDA level peaked at early disease stages, among PD patients. These results suggest increased oxidative damage and decreased anti-oxidant capacity in peripheral blood, and a significant correlation between leucocyte 8-OHdG level and disease severity in PD.