To evaluate the renal toxicity of intravenous administration of ioversol and iohexol, the urinary N-acetyl-beta-glucosaminidase (NAG) to creatinine ratio was measured before and after drip infusion pyelography. Thirty patients received intravenous ioversol and 29 patients received iohexol. The urinary NAG to creatinine ratio tended to increase after respective contrast media: 5% increase in the ioversol-treated, and 8% in the iohexol-treated patients. There were no significant differences in these values; the nephrotoxicity of ioversol appeared to be just as insignificant as that of iohexol.