A non-ionic, monomeric, low-osmolar contrast medium, iopentol (Imagopaque, Nycomed Imaging AS, Oslo, Norway) has been compared with iohexol (Omnipaque, Nycomed Imaging AS, Oslo, Norway) in a double-blind, randomized, parallel-group trial in children. The aims of the study were to compare the safety and radiographic efficacy of iopentol 350 mg I/ml versus those of iohexol 350 mg I/ ml in pediatric cardioangiography. Seventy-three children, of whom 35 received iopentol and 38 iohexol, were included in the evaluation. The quality of overall diagnostic information was excellent or adequate in all patients. There were no statistically significant differences between numbers of patients reporting adverse events nor number of patients reporting discomfort in the two groups. Three patients in the iopentol group and two patients in the iohexol group reported adverse events. Heat sensation was reported by 4 patients in the iopentol group and 5 patients in the iohexol group. Following injection of contrast medium, there were no differences between the groups regarding ECG, heart rate and systolic blood pressure at the site of injection. Iopentol was demonstrated to be as effective, safe and well tolerated as iohexol in pediatric cardioangiography.