Since the pharmacology of phenoltetrachlorphthalein was studied in 1910 by Abel and Rowntree,1who found that this dye, under normal conditions, was excreted entirely by the liver, numerous efforts have been made to use it for testing hepatic function. Previous methods have depended on the determination of the excretion of this dye in the stools or duodenal contents. The fallacies and impracticabilities of these procedures, which have prevented their wide clinical usage, have been previously pointed out.2In an attempt to avoid the drawbacks attendant on estimating the excretion of tetrachlorphthalein, I devised a method based on the ability of the liver to remove the dye from the blood stream. I have studied this method experimentally,2and have shown that after the intravenous injection of a given dose per body weight, the dye normally leaves the plasma very rapidly and with remarkable uniformity. Striking degrees of retention