Acute contrast medium-induced nephrotoxicity was estimated in 3%-12% of patients receiving cardiac angiography, especially in advanced age, renal insufficiency and diabetic patients. As intrinsic renal antioxidant enzyme activities may play a crucial role in defence against renal oxidant injury, this study was designed to investigate the acute effect of ionic high osmolar diatrizoate meglumine/diatrizoate sodium on renal antioxidant activities in normal or streptozotocin (STZ)-induced diabetic rats at two time points (1 h and 24 h). A total of 40 Wistar rats were separated to normal and STZ-induced diabetic groups. Ten of each group were injected with diatrizoate (10 ml/kg) via tail vein and 10 with 10 ml/kg of 0.9% NaCl as control. This study shows that diabetic rats had higher renal glutathione peroxidase (GPx) activities than those of normal rats. GPx activities decreased significantly after diatrizoate injection at the first hour (717.4+/-104.0 to 578.6+/-92.1 mU/mg in the diabetic group, 466.4+/-30.6 to 371.4+/-75.5 mU/mg in the normal group, all P=0.032) but the difference faded 24 h later. The increase of superoxide dismutase (SOD) activities was enhanced (673.5+/-100.2 to 750.4+/-129.8 U/mg, P=0.04) in the normal group, but not in the diabetic group (624.1+/-156.6 to 671.1+/-136.7 U/mg, P=0.15) after diatrizoate injection at the first hour. At 24 h, renal SOD activities were still significantly higher in the diatrizoate injection group. In summary, intrinsic renal antioxidant activities are adapted in STZ-induced diabetes and ionic high osmolar diatrizoate could modify their activities. Furthermore, diabetics have abnormal response of renal antioxidant activities by contrast media and are at risk for contrast-mediated nephrotoxicity.