Oxidative stress and generation of reactive oxygen species are believed to be implicated in Parkinson's disease (PD). Erythrocyte activity of superoxide dismutase (SOD) and catalase, the blood glutathione system, and plasma levels of thiobarbituric-acid-reactive substances (TBARS) were measured in 80 PD patients. These biochemical parameters were also measured in 29 age-matched controls. Patients with PD had significantly higher red blood corpuscle (RBC) activity of SOD. The mean RBC activity of catalase in PD patients did not differ significantly from those of controls. RBC catalase activity was significantly lower in advanced cases of PD compared to early cases. Oxidized glutathione was significantly higher in RBCs of PD patients, although there were no changes in total glutathione and reduced glutathione compared to controls. TBARS content was increased in patients with PD. Levodopa therapy, age and duration of illness did not significantly influence the measured parameters. Our study supports the previous hypothesis that oxidative stress is implicated in the pathogenesis of PD. Perspectives for treatment of PD in the future could include antioxidant therapy. Copyright 2007 S. Karger AG, Basel.