Behcet's disease (BD) is a chronic, progressive disorder that affects many systems of the body including the eye. The aim of this study was to assess whether the increase in oxidative stress in the affected tissues is reflected by lipid peroxidation and to check for alterations in antioxidants and antioxidant enzyme activities in patients with BD. Erythrocyte antioxidant potential (AOP), glutathione (GSH) and GSH-dependent enzymes (glutathione peroxidase (GSH-Px), glutathione reductase (GRD) and glutathione-S-transferase (GST), catalase (CAT), Cu-Zn superoxide dismutase (Cu-Zn SOD) activities, malondialdehyde (MDA) and some trace elements (zinc, Zn; copper, Cu; manganese, Mn) levels in men with BD. Erythrocyte CAT, GSH-Px activities, MDA, GSH, AOP and serum Zn values were significantly lower in patients with BD than in the control group. However, erythrocyte Cu-Zn SOD, GRD activities, erythrocyte sedimentation rate (ESR), serum C-reactive protein (CRP) and Cu values were significantly higher in patients with BD than in the control group, but GST activity and serum Mn values were unchanged. In conclusion, our results confirm the presence of oxidative stress in patients with BD and suggest that the severity of BD may arise from impaired antioxidant mechanisms. Therapy with antioxidants may lead to the increase in the antioxidant defense system and thus improvement in clinical symptoms.