Pancreaticobiliary maljunction is frequently associated with biliary carcinoma, whether or not there is choledochal dilatation. In this anomalous condition, pancreatic juice regurgitates and the mixture of bile and pancreatic juice stagnates in the biliary tree. In cystic choledochal dilatation, cancers arise, mainly in the dilated bile ducts, while in patients not having cystic dilatation, tumors arise in the gallbladder. Gallbladder bile and/or bile duct bile from fifteen cases of pancreaticobiliary maljunction, including five cancer patients, was analysed biochemically and compared with control bile from 6 patients with a normal pancreaticobiliary junction. Bile levels of pancreatic enzymes were extremely high in the anomalous junction group. In the bile duct bile from patients with cystic choledochal dilatation with pancreaticobiliary maljunction, the concentrations of deoxycholic acid (DCA), lithocholic acid (LCA) and unconjugated bile acid fractions were increased regardless of the presence of cancer. Increases of these bile acid fractions, which are known to have a cancer-promoting effect, were also seen in gallbladder bile from the cancer patients without cystic dilatation.