Excretion of urinary N-acetyl-beta-glucosaminidase (NAG), lactate dehydrogenase (LDH), alkaline phosphatase (ALP) and gamma-glutamyltransferase (gamma-GT) was studied following single intravenous administrations of a non-ionic monomeric contrast medium (iohexol) at doses of 5.0, 7.5, 10.0 and 12.5 g iodine/kg body wt in rats. Measurements of urinary enzymes, serum urea nitrogen and serum creatinine were carried out on the 2nd, 3rd, 4th and 8th days after treatment. Histological examinations of kidneys were performed on days 3 and 8. From 5.0 g iodine/kg onwards urinary NAG showed a dose-dependent and significant (multiple comparison, alpha = 0.05) increase in the first 18-h urine samples after application. A significant increase in urinary LDH could be observed only at the highest dose of 12.5 g iodine/kg. All other biochemical parameters showed no differences when compared to the control group. The dose-dependent increase in lysosomal NAG correlated with the histological findings, i.e. there was dose-dependent vacuolization of proximal tubular cells, so-called 'osmotic nephrosis'.