It has been suggested that among the factors that lead to neuron loss in substantia nigra in Parkinson's disease are stimulation of lipid peroxidation and deficiency of glutathione and glutathione peroxidase. In this study, the effect of neurodegenerative changes on plasma and erythrocytes were investigated in Parkinson's disease. The results were compared with age-matched controls. Increase in plasma lipid peroxide levels and erythrocyte susceptibility to lipid peroxidation were observed in patients with Parkinson's disease. Erythrocyte catalase activities were not changed whereas glutathione levels and glutathione peroxidase activities were decreased.Our results suggest that erythrocyte membrane integrity is impaired in Parkinson's disease. We are carrying out more detailed studies to determine whether this is related to neurodegenerative changes observed in Parkinson’s disease and whether parkinsonians will benefit from antioxidant treatment.