The purpose of the present study was to evaluate the safety and efficacy of iopentol 350 mg I/ml (Nycomed AS, Oslo, Norway) compared to iohexol 350 mg I/ml (Nycomed AS, Oslo, Norway), in patients undergoing coronary cineangiography and left ventriculography. Fifty patients were randomly allocated to each group. The groups were comparable regarding demographic data and number and volume of contrast medium injections. There were no significant differences between the two treatment groups regarding effects on hemodynamic, electrocardiographic or clinical laboratory parameters. Adverse reactions related to the contrast media were all of mild intensity, and with nearly equal occurrence in the two groups. There were, however, three serious events which were considered to be disease- of procedure-related. Discomfort associated with injection was slightly less with iopentol than with iohexol (p=0.023). The efficacy of both media was similar, with diagnostic visualization judged to be of good or excellent quality in all patients.