Plasma nitrotyrosine and nitrite/nitrate levels as markers of nitrosative stress and plasma malondialclehyde (MDA) and protein carbonyl as markers of oxidative stress were determined in patients with Beh et disease (BD). To evaluate the balance between oxidant and antioxidant systems in these patients, we measured erythrocyte lysate CuZn superoxide dismutase (CuZn SOD) activity, plasma sulffiydryl (SH) values and total antioxidant activity. We also determined levels of plasma C-reactive protein (CRP), a key marker of inflammation, and compared them with those of healthy subjects. We found plasma nitrotyrosine levels of BD patients to be increased, indicating that nitrosative stress may occur in these patients. Plasma MDA and CRP levels in BD patients were found to be significantly higher than those in control group. However, plasma SH levels were decreased. No changes were observed in the other measured parameters of the patient group compared with the controls. These data suggest the possible involvement of nitric oxide (NO) together with reactive oxygen substances (ROS) in the pathogenesis of BD.