In the past three years we have been aided in our studies of the pathologic physiology of the biliary tract associated with surgical lesions by being able to visualize the common and hepatic ducts under the fluoroscope and by roentgenographic studies after injection into the common duct through a T tube of nonirritating substances which are opaque to roentgen rays.1Briefly stated, the choledochograms so obtained will reveal the presence of (1) any narrowing of the common bile duct and persisting pancreatitis, with an abnormally patent duct of Wirsung, (2) an overlooked stone in the common bile duct, (3) spasm or stenosis of the sphincter of Oddi, and (4) carcinoma of the ampulla of Vater or of the head of the pancreas. In an effort to determine the influence of the sphincter of Oddi in this respect, studies of the pressure within the common duct were carried out in