Objective: The pathogenesis of Behcet's disease ( BD) may be related to excessive production of reactive oxygen species, activated neutrophils, and T lymphocytes. The goal of this prospective study was to investigate whether there is any relationship among the oxidant/ antioxidant system and nitric oxide ( NO) and malondialdehyde (MDA) levels in patients with BD and its subtypes: complete Behcet's disease (CBD) and incomplete Behcet's disease (ICBD), with or without ocular disease. Methods: Thirty-two patients and 26 age- and sex-matched healthy control subjects were evaluated for NO and MDA levels and antioxidant enzyme activities. The patients with BD were divided into two subgroups: those with and without ocular disease. Twelve patients with CBD and 4 patients with ICBD had ocular disease. The serum NO level was determined by Griess reaction. The MDA level was detected by thiobarbituric acid reaction. Superoxide dismutase ( SOD) and glutathione peroxidase (GSH-Px) activities in serum were analyzed with spectrophotometric methods. Results: Increased MDA levels but decreased GSH-Px activities in plasma were observed in BD patients with all subtypes, as compared with controls. Concerning the presence of ocular disease and the subtype ( CBD or ICBD) compared with each other, there were no significant differences in MDA or NO serum levels and SOD or GSH-Px enzyme activities. Conclusions: Serum NO levels and SOD enzyme activities were not significantly changed in patients with BD and its subtypes; however, a remarkable decrease of GSH-Px enzyme activity and increase of MDA levels were found. Copyright (C) 2004 S. Karger AG, Basel.