In 6 patients with no apparent kidney function the elimination of contrast medium was examined using 125I-labelled diatrizoic acid. Also blood level time curves and concentrations of dialysate were measured, showing a biexponential fall. The kinetic data established by computer-aided analysis according to the two-compartment model yielded elimination values not achieved by a healthy kidney; however a maximum elimination rate of 80.7 +/- 4.7% of the dose administered was calculated for a dialysis period of more than 10 hours. As the contrast medium plasma level was reduced the efficacy of haemodialysis fell.