SummaryThe authors compare the plasmatic and urinary clearances of radiohippuran and radiohypaque after a single intravenous injection, with the urinary clearances of PAH and inulin.They find that the urinary clearances of radiohypaque are in good agreement with those of inulin. The plasmatic clearances of radiohypaque are corrected by a factor of 20 ml/min which was found to be the plasmatic clearance of two anephric patients; it is shown that the so corrected plasmatic clearances agree fairly well with those of inulinIt is shown that the urinary and plasmatic clearances of hippuran are smaller than the urinary clearances of PAH. Furthermore, the correlation between the plasmatic clearances of hippuran and those of PAH is poor. Therefore it is felt that hippuran, as commercially delivered in Europe, can not be used for the determination of renal blood flow.