Erythrocyte survival was studied in 51 patients with severe renal failure and in 9 control sub-jects. In acute renal failure, 51Cr-labelled red cell life span was nearly always shortened, the mean survival of the group of 14 patients with renal tubular necrosis being 35 days, that of the 6 patients with acute or subacute glomerulonephritis being 48 days, and of the 11 patients with malignant hypertension 34 days, as compared with the mean life span of 98 days in the control group. In chronic renal fail-ure, erythrocyte survival was frequently shortened, the mean red cell life span being 63 days. Erythrocytes from 3 oliguric, severely uremic patients had a reduced survival when injected into normal recipients. Red cell destruction appeared to occur at an intravascular site, for there was no excessive accumulation of 51Cr in the liver or spleen, and, in patients with more severe hemolysis, serum haptoglo-bin was diminished. Shortened erythrocyte survival was the result of premature ageing as indicated by the linear decline of erythrocyte radioactivity. Comparison of the rate of hemolysis with severity of uremia or acidosis, presence or absence of oliguria, and the nature of the renal lesion showed that the most potent factor responsible for this premature ageing was closely related to rapidly worsening uremia, and was probably a chemical substance which depends upon an adequate urinary volume for its excretion. Blood-volume was mea-sured in 46 patients with renal failure. Red cell mass was reduced, the mean values for each group of patients being 15 to 19 ml/kg body weight, as compared to 29 ml/kg for the control group. Total blood-volume was normal, and plasma-volume slightly increased.
