In order to explore the relationship of lipid peroxidation and long-term complications in diabetes mellitus, we tested LPO (lipid peroxides), FPG (fasting plasma glucose), cholesterol, triglycerides, and HDL (High Density Lipoprotein) levels of 44 healthy controls and 83 type II diabetics. Mean plasma LPO value of healthy controls was found to be 2.55±0.51 nmol/ml. This value seemed to increase by age, but no sexual difference was observed (in women 2.46±0.53, in men 2.66±0.48 nmol/ml, mean+S.D.). Comparison of plasma LPO values showed a significant difference between healthy controls and total diabetics (4.05±1.24 nmol/ml), complicated group (4.46±1.32 nmol/ml) and non- complicated group (3.49±0.80 nmol/ml), (p<0.001). According to these data we concluded that increased lipid peroxidation in diabetes mellitus may induce the onset of long-term complications.