The recent modification by Rosenthal1of the phenoltetrachlorphthalein method of testing liver function has marked another advance in our efforts to understand the functional competence of this complex organ. After the preparation of the dye by Orndorff and Black2in 1908, and the contribution of Rowntree and Abel3in 1909 showing that this dye is withdrawn from the blood solely by the liver, a long series of investigators have reported on its merits in testing liver function, first by the stool and later by the duodenal tube method. Now Rosenthal has introduced a new method based on the ability of the liver to remove the dye from the blood stream in a given time. We have made sixty-seven separate determinations of liver function, using the Rosenthal technic. His method was then used as a standard for comparison with the other most important methods of estimating liver function,