The aim of this study was to investigate the influence of homocysteine (hcy) levels on endothelial function by the method of brachial artery ultrasonography and their relation with microvascular complications in type 2 diabetes mellitus (T2DM) patients without macrovascular disease. Fifty-nine T2DM patients with a mean age of 53.4+/-8.6 years and diabetes duration of 8.1+/-6.2 years and 16 healthy controls with a mean age of 47+/-14.5 years were included in the study. Endothelialdependent and endothelium-independent flow-mediated dilatation (FMD) were evaluated via brachial artery ultrasonography. Fasting plasma glucose (FPG), glycosylated haemoglobin (A1c), lipid profile, hcy, B12 and folic acid levels were measured. Diabetic patients and control group individuals were compared with regard to the laboratory values and brachial artery vascular reactivity. Factors influencing endothelium-dependent FMD were investigated with linear regression analysis. Age, gender, body mass index, lipid profiles and hcy levels were similar in both groups (p>0.05). Endothelium-dependent FMD percentages were significantly lower in diabetics than in the control group (7.7+/-5.9 vs. 11.7+/-7.1%, p<0.05). Endothelial-independent FMD percentage was similar for both groups (p>0.05). The upper limit of the reference hcy value was found to be 12.6 micromol/l in the control group. In the diabetic group, hcy levels were high in 33 patients and normal in 26 patients. No difference was detected between the patients with high hcy levels and those with a normal level with regard to endothelium-dependent and endothelium-independent FMD values (p>0.05). Mean hcy levels were 16+/-1.7 and 13.3+/-4.3 micromol/l in T2DM patients with microvascular complication and those with no microvascular complication, respectively (p<0.05). Regression analysis revealed that the main factors influencing the endothelial-dependent FMD were FPG, total cholesterol (TC), triglycerides (TG) and high-density lipoprotein (HDL-C) levels (p<0.05, p=0.05, p=0.05, p=0.02, respectively). Hcy, folic acid and B12 values did not influence endothelium-dependent FMD (p>0.05). Diabetes duration and A1c levels were close to being significant although they did not reach statistical significance (p=0.07 and p=0.08 respectively). Hcy levels have no effect on endothelium-dependent and endothelium-independent FMD in T2DM patients without macrovascular complications. The influence of classical atherogenic factors (such as FPG, TC, TG and HDL-C levels) on endothelium functions, detected with endothelium-dependent FMD, is greater.