In this phase I study, safety, tolerance and pharmacokinetics of iodixanol 300 mg I/ml, were evaluated in 40 healthy male volunteers using four dose levels. No clinically important influences on renal function parameters, hemodynamics, ECG or clinical-chemical parameters in blood and urine were observed. 17 adverse events including discomfort were reported, but only three of them (sensation of warmth) were classified as related to iodixanol. CT-investigations revealed a dose-related, reversible increase in kidney cortex density. However, iodixanol caused no changes in glomerular function, and the increase in excretion of tubular enzymes was less than caused by other nonionic x-ray contrast media. Further investigations will focus on the safety and efficacy of iodixanol in patients.