The diameter of extrahepatic and intrahepatic bile ducts was measured on 50 normal retrograde cholangiograms and on the cholangiograms of 109 post-cholecystectomy patients undergoing endoscopic retrograde cholangiopancreatography: 70 of the post-cholecystectomy patients had a normal cholangiogram and 39 had retained stone or biliary stricture, of whom 17 were jaundiced. Biliary diameter at all points measured was greater in the post-cholecystectomy patients with no biliary lesion than in normals, and further increased in the presence of pathology (e.g. retained stone). The extent of overlap in biliary diameter between all these three groups is so great that measurement of bile duct calibre cannot separate patients with retained stone from post-cholecystectomy patients without retained stone, or from patients with an entirely normal biliary tree, even in the presence of obstructive jaundice. Methods of evaluating the biliary tract which rely on the measurement of bile duct diameter (e.g. ultrasound) are therefore of limited value in the investigation of post-cholecystectomy patients.