To the Editor.
—As Dr. Willard noted, we measured the red blood cell (RBC) volume with sodium chromate Cr 51 autologous RBC only. There was no loss of 51Cr-labeled autologous RBC during the one-hour post-infusion period in our patients without splenomegaly. With iodinated I 125 serum albumin, the plasma volume was overestimated in patients. The measurement of RBC volume with 51Cr autologous RBC and plasma volume with iodinated I 125 serum albumin overestimated the blood volume in patients. The "f" value, which is used to correct the peripheral venous hematocrit to the total body hematocrit, has a wide range when derived from the plasma volume measured by iodinated I 125 serum albumin, the 51Cr RBC volume, and the peripheral venous hematocrit. The f value for all patients derived from the 51Cr volume, iodinated I 125 cold agglutinin plasma volume, and peripheral venous hematocrit was about