Iodixanol (Visipaque) is a dimeric, non-ionic iodinated contrast medium that is isotonic with blood at all clinically relevant concentrations. Iodixanol was compared in a randomized, double blind, parallel group, phase III multicentre trial with a monomeric, non-ionic contrast medium, iohexol (Omnipaque), at two concentrations assessing safety, tolerability and radiographic efficacy during contrast enhanced gastrointestinal radiography examinations of children. 154 children entered the trial; 152 formed the safety population and 147 the efficacy population. All examinations were performed following standard departmental practice. Children were assigned into either a high or low concentration group (iodixanol, 150 mgI ml(-1) and 320 mgI ml(-1) vs iohexol, 140 mgI ml(-1) and 300 mgI ml(-1)). The primary outcome measure for efficacy was the overall quality of visualization, which was assessed using a 100 mm visual analogue scale (VAS). The secondary efficacy variables assessed were quality of contrast opacification, mucosal coating and overall quality of diagnostic information. Safety evaluation involved patient follow-up for at least 48 h. Taste acceptance was also assessed. There was no statistically significant difference between the two contrast media with regard to the primary and secondary efficacy variables assessed, although higher ratings were observed for iodixanol. The 100 mm VAS score overall was 86 mm for iodixanol and 82 mm for iohexol (95% confidence interval -2.56, 10.42). The frequency of adverse events was lower for patients receiving iodixanol. Adverse events, mainly diarrhoea, occurred in 12 patients (16.2%) in the iodixanol group and 28 patients (35.9%) in the iohexol group. This reached statistical significance (p=0.006). Overall, iodixanol is well suited for examinations of the gastrointestinal tract, giving good efficacy results and fewer adverse events than iohexol.