Since the beginning of our work on cholecystography,1an effort has been made to find a substance which would not only prove practical for visualizing the gallbladder but which would also give sufficient color to the blood serum to permit the use of it for a test of hepatic function, in a manner similar to the test devised by Rosenthal2with the use of phenoltetrachlorphthalein. It will be recalled that Rosenthal improved the previous method of use of this substance by noting the amount of the dye retained in the serum after given periods instead of the amount which passed into the stools. His principle, therefore, was to estimate the hepatic function by determining the amount of dye that failed to pass through the liver in a given time instead of by determining the amount that actually passed through. After we found that cholecystography was a practical procedure