1. The clearance of isotopically labelled sodium diatrizoate by haemodialysis was measured in vitro, with simulated extracellular fluid, and in vivo in eleven patients, at varying rates of fluid or plasma flow. Clearance was also measured in five patients undergoing peritoneal dialysis. In all instances simultaneous measurements of urea clearance were made and the diatrizoate/urea clearance ratio was calculated.
2. In haemodialysis studies, diatrizoate and urea clearances showed a linear increase with increasing ‘extracellular fluid’ or plasma flow through the dialyser while the diatrizoate/urea clearance ratio fell.
3. The clearance of diatrizoate in vivo was slightly less than clearance in vitro at corresponding flow rates, but the diatrizoate/urea clearance ratio showed no significant difference.
4. Diatrizoate and urea clearances during peritoneal dialysis were very much lower than during haemodialysis but the diatrizoate/urea clearance ratios were within the same range.
5. The rapid removal of diatrizoate in patients with renal failure requires haemodialysis.