Nephrotoxicity is a common side effect of intravascular contrast media (CM). Although nephrotoxicity of ionic CM has been widely demonstrated, recent studies suggest that newer and more costly non-ionic agents are not less nephrotoxic. We studied the hemodynamic, hematologic and nephrotoxic effects of CM prospectively in 38 patients (ages six months-16 years) with or without risk factors predisposing to nephropathy and compared ionic and non-ionic CM. We performed intravenous urography (IU) with a ionic CM, sodium meglumine diatrizoate (n = 18) and a non-ionic CM, iohexol (n = 20). The patients were divided into three groups according to glomerular filtration rate (GFR) [GFR < or = 50 (n = 9), 50-80 (n = 13), > or = 80 ml/min/1.732 (n = 26)]. Eleven patients had risk factors for nephropathy. Blood pressure, heart rate, ECG, urine and blood samples were obtained 24 hours and one hour before as well as one, 24, and 48 hours after CM infusion. Although a significant increase was found in urine specific gravity, protein/creatinine ratios and serum Na and creatinine levels, the increased levels were within normal limits. We observed a significant reduction in Hb and Htc and urinary prostaglandin E1 levels. Many of the changes observed in the urine and serum values after the use of CM were minor, insignificant and transient, later returning to their initial values. The GFR levels, the presence of risk factors and the use of ionic vs. non-ionic CM had no effect on the results. The elevated urinary basal beta-2-microglobulin levels further increased after CM in patients with low GFRs. It was concluded that non-ionic CM was not superior to ionic CM in patients with GFRs greater than 50 ml/min regardless of predisposing risk factors. One of the non-invasive radiological methods is advised instead of IU in patients with low GFRs.