A total of ninety three patients with biliary tract disease were studied to determine the concentration of the pancreatic enzymes, amylase and lipase, in bile obtained from the gallbladder and/or common bile duct. Of seventy gallbladder bile samples, amylase levels were higher than actual or predicted serum levels in 87 per cent, while bile lipase were higher than serum lipase values in 66 per cent. Bile obtained from the common bile duct had enzyme concentrations which fluctuated from values similar to those in serum to remarkably high levels. This suggests that pancreatic enzymes enter the biliary system through a common terminal ampulla which is known to exist in 60 to 90 per cent of human subjects. The premise is advanced that pancreatic enzymes may initiate inflammatory changes in the gallbladder and could play a role in gallstone formation by altering the constituents which maintain cholesterol in a soluble state. Biliary reflux of pancreatic enzymes could play a role in the pathogenesis of some cases of cholecystitis can cholelithiasis.