Meglumine sodium diatrizoate (Urografin), iopamidol, and iohexol were compared in a double-blind, randomized study of 287 patients undergoing elective cardiac angiography. Ninety-six patients received Urografin, 98 received iopamidol, and 92 received iohexol. The groups were similar in all respects. Variables measured before and after contrast injection were left ventricular end-diastolic pressure (LVEDP), lefl ventricular systolic pressure (LVSP), systolic arterial pressure (SAP), RR, PR, and QTc intervals, QRS duration, ST segment change greater than 2 mm, arrhythmias, and symptoms. The adequacy of coronary and ventricular opacification was assessed by two experienced observers. Following left ventriculography, small rises in LVEDP occurred with iopamidol and iohexol (mean f SD: 18 f 7 to 21 f 7 mmHg) and a moderate fall in LVSP with Urografin (150 f 32 to 133 f 32 mmHg). Following coronary angiography there was a progressive fall in SAP (130 f 26 to 117 f 30 mmHg) and prolongation of RR intervals (900 f 138 to 1,266 2 692 msec) and QTc (440 f 61 to 471 2 73 rnsec) and QRS duration (87 f 25 to 100 f 27 msec) with Urografin. There was a small fall in SAP with iopamidol(138 2 25 to 128 f 27 mmHg) and prolongation of QRS duration with iohexol (85 f 29 to 90 f 24 msec). Other parameters were not significantly affected. Frequent bradyarrhythmias (sinus pause 14.5%, asystole 6%) and ST segment depression occurred following Urografin. Urografin was less well tolerated, with 10% of patients experiencing severe nausea or vomiting and 30% of patients experiencing extreme heat sensation. Differences between iohexol and iopamidol were minor. Coronary and left ventricular opacification were satisfactory and not significantly different between the groups. lopamidol and iohexol have fewer adverse hemodynamic, electrocardiographic, and symptomatic effects, and their use in preference to Urografin is advocated.