The aim of this study was to compare the safety, tolerance, and diagnostic efficacy of iomeprol 350 mg I ml-1, iohexol 350 mg I ml-1, and iopamidol 370 mg I ml-1 in 90 adult patients undergoing intravenous urography. Radiographs obtained 5, 10 and 15 min after contrast injection were blindly graded for quality on a four point scale as: 0, non-diagnostic; 1, diagnostic but of limited quality; 2, diagnostic and of good quality; 3, fully diagnostic and of very good quality. The sum of these scores indicated the overall diagnostic quality (0-4, non-diagnostic; 4-8, diagnostic; 9-12, good or excellent). Contrast tolerability was evaluated by discomfort (heat or pain) associated with injection of the test compounds, and patients were monitored and questioned for adverse experiences. The quality of the individual radiographs was assessed as diagnostic and good or fully diagnostic and very good in most cases, with no significant differences between the three study groups, and overall scores were predominantly good or excellent (p = 0.55). All adverse reactions were transient and non-serious, and most of them were reported as mild in intensity. There were no significant differences between the three groups for heat sensation (p = 0.29). Pain at the injection site was reported only in the iohexol group (p = 0.104). It is concluded that iomeprol 350 mg I ml-1 is at least as safe and effective as iohexol 350 mg I ml-1 or iopamidol 370 mg I ml-1 when used for intravenous urography.