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 examine the effects of nitric oxide synthase activity (NOS), nitric oxide and homocysteine (Hcy) levels in patients with active BD. Included in this study were 18 male BD patients and 16 male healthy volunteers as controls. Erythrocyte NOS activity, F, erythrocyte sedimentation rate, serum C-reactive protein, and plasma Hcy values in the patients with BD were significantly higher than those of the control group. Our results show that these parameters play a major role in the inflammatory reactions observed in BD.