OBJECTIVE Low-osmolality contrast agents, ionic and nonionic, are being used more frequently in coronary arteriography. A new nonionic contrast agent, iopromide, has recently become available for use in clinical trials. The purpose of this phase II-phase III Food and Drug Administration (FDA) trial was to compare the side effects and diagnostic quality of iopromide with iohexol and iopamidol for coronary arteriography and left ventriculography. METHODS Two separate double-blind trials were performed using iopromide and comparison nonionic contrast agents. In the first trial, 41 patients were randomized to receive iopromide or iopamidol. The second trial was a three-center trial involving 120 patients, of whom half received iopromide (370 mg I/mL) and the other half received iohexol (350 mg I/mL). In a third study, 26 patients received iopromide (370 mg I/mL) according to an open-label design. RESULTS Comparison of iopromide with the other agents revealed that there were no significant differences in adverse events between iopromide and the comparison agents. Most adverse reactions were mild or moderate in severity in all patient groups. There was no difference in the patients' perceptions of heat and pain and no statistically significant difference in systolic or diastolic blood pressure at baseline, at 30 to 60 minutes, or at 24 hours after the procedure. No difference was found in the biochemical or hematologic analysis at baseline or at 24-hour follow-up. No difference between the contrast media groups in terms of the quality of the left ventriculogram or the quality of the coronary arteriography was noted. CONCLUSIONS Compared to the other nonionic agents, iopromide showed no statistically significant differences in terms of safety or efficacy.