Vascular complications, as a consequence of atherosclerosis, are the main causes of morbidity and mortality in diabetes. Low density lipoprotein (LDL) oxidation is accepted as a relevant pathogenic mechanism in atherogenesis. The aim of this work was to study the relationship between lipid peroxidation (LPO) and metabolic control. LPO was evaluated in 40 type 2 normolipidemic diabetic patients by measuring thiobarbituric acid reactive substances (TBARS), in the plasma, using malondialdehyde (MDA), end product of the oxidation of polyunsaturated fatty acids, as a standard. Fast blood glucose (FBG), serum total cholesterol (TC) and serum triglycerides (TG) were evaluated by routine methods. Fructosamine (FR) was measured by the nitroblue tetrazolium (NBT) colorimetric test. An elevated level of lipid peroxides (P < 0.001) was observed in the plasma of diabetic patients (4.51 +/- 1.29 nmol/ml) as compared to normal subjects (3.54 +/- 1.00 nmol/ml). Lipid peroxides did not correlate with the FR levels, nor with FBG, TC and TG. These results show an increase of LPO in type 2 normolipidemic diabetic patients. Probably the mechanism for higher lipid peroxide levels in diabetes is multifactorial. Our study supports the hypothesis of a role of oxidative stress in diabetes independently of the lipid serum content.