The exact pro-and antioxidant status in schizophrenic patients is still not clear. To add a new insight to the question, changes in the erythrocyte lipid peroxidation products (MDA), levels of glutathione (GSH), ascorbic acid and plasma vitamin E (nonenzymatic antioxidant parameters) and activities of antioxidant enzymes superoxide dismutase (SOD), glutathione peroxidase (GPX) and catalase in erythrocytes were studied in 48 schizophrenic patients and 48 healthy subjects. It was observed that there was a significant increase in erythrocyte MDA levels and activities of SOD and GPX and a significant decrease in erythrocyte GSH, ascorbic acid, plasma vitamin E levels and catalase activity in patients with schizophrenia, when compared to controls. The results of our study have shown higher oxygen free radical production, evidenced by increased levels of MDA and decreased levels of GSH, ascorbic acid, vitamin E and catalase activity, which supports the oxidative stress in schizophrenic patients. The increased activities of antioxidant enzymes may be a compensatory regulation in response to increased oxidative stress. The decreased concentrations of the glutathione and antioxidant vitamin status support the hypothesis that lipid peroxidation is an important causative factor in the pathogenesis of schizophrenia. These data reveal that antioxidant defence mechanisms might be impaired in schizophrenic patients. These findings also provide a theoretical basis for the development of novel therapeutic strategies, such as antioxidant supplementation. This may suggest the hope for use of antioxidants in clinical trials to prevent and treat schizophrenic patients.