Iodixanol (Visipaque, Nycomed, Oslo, Norway) is an iodinated contrast medium in the form of a non-ionic dimer which is iso-osmolar with plasma at all iodine concentrations. There is little evidence regarding its renal tolerance in renal impairment. We therefore undertook a prospective randomized comparison of iodixanol and the non-ionic monomer iohexol (Omnipaque, Nycomed, Oslo, Norway). The serum creatinine was measured pre- and post-angiography in a series of in-patients to establish whether there was any clinically detectable evidence of superiority of iodixanol over iohexol in this high risk group. 8/54 (15%) patients in the iodixanol group had a rise in creatinine of > 10% in the week following angiography compared with 15/48 (31%) in the iohexol group (p < 0.05). The creatinine rise was positively correlated with the dose of both contrast media. These results suggest that iodixanol may be slightly less nephrotoxic than iohexol.