This study evaluated the effect of streptozotocin (STZ) induced diabetes on autoxidizability of VLDL + LDL fractions, plasma lipid peroxide and total thiol levels. Increased susceptibility to autoxidation of VLDL + LDL was observed following STZ treatment. Plasma lipid peroxide levels were found significantly higher in diabetic rats. However, plasma total thiol levels were observed decreased in experimental diabetes. In conclusion, the balance of prooxidant and antioxidant in plasma is disturbed by STZ treatment.