Nephrotoxic effect of ionic and non-ionic contrast media was examined in a doubleblind study by evaluation of serum creatinine, blood urea nitrogen, urine volume, urinary protein excretion and erythrocyturia before and after selective renovasography. In 19 of 22 patients reliable results were obtained. With optimal hydration before and after renovasography no significant differences between both administered contrast media (Rayvist 300 and Omnipaque 300) could be found by evaluation of the aforementioned parameters. In 3 patients with preexistent proteinuria (greater than 200 mg/l) urine protein excretion remained at the same or a lower level after application of the non-ionic contrast medium Omnipaque 300. Three patients with proteinuria tended to increase the proteinuria after administration of the ionic contrast medium (Rayvist 300) up to 48 h after angiography indicating a higher nephrotoxic potential of ionic contrast media in patients with preexistent renal disease. The constant values of urine volume and serum creatinine indicate an absence of clinically relevant nephrotoxicity of both contrast media in this study when administered in well-hydrated patients. This emphasizes the importance of sufficient hydration in prophylaxis of nephrotoxic effects, especially in patients with risk factors.