The renal effects of the new dimeric non-ionic contrast medium Visipaque were investigated in healthy volunteers and in patients with severe renal failure. Visipaque caused no changes in GFR after i.v. injections to healthy volunteers and less changes in tubular function than monomeric CM. Small and transient changes in GFR were observed in predialytic patients both with Visipaque and with the monomeric Omnipaque. A delayed excretion of both CM was observed in these patients and no differences were observed between the two CM as far as tubular enzymes excretion and glomerular functional parameters are concerned. More iodine was retained in the kidney after Visipaque than after monomers, but this was not correlated with changes in tubular parameters and in GFR. Thus, Visipaque was well tolerated in subjects with normal renal function and in patients with severe renal failure.