Hyperhomocysteinemia has been identified as independent risk factor for early atherosclerotic vascular disease. The purpose of our study was to investigate the plasma homocystein (Hcy) concentrations and its relationship with lipid peroxidation as thiobarbituric acid reactive substances (TBARS) and nitric oxide (NOx; nitrite plus nitrate) concentrations in age-matched non-obese (n=55) and obese (n=60) female subjects with type 2 diabetes mellitus. Non-obese diabetic patients have significantly higher plasma tHcy and TBARS (p < 0.001 and p < 0.001), and significantly lower NOx concentrations than the controls (n=25) (p < 0.001). The plasma tHcy and TBARS concentrations were higher and nitric oxide concentrations were lower in obese diabetics than in non-obese diabetics (for each comparison; p < 0.001). Correlation analysis demonstrated that there was a significant positive correlation between tHcy and TBARS (r=0.452, p < 0.01) in diabetics groups. There was no significant correlation between tHcy and plasma NOx, insulin and blood pressure. We thought that Hcy might have a permissive role on the endothelium damage through free radical generating systems and the presence of obesity the free radical induced-damage has been elevated in diabetic patients.