The gallbladder is traditionally regarded as an absorptive organ. There is increasing evidence that the gallbladder mucosa can have a secretory function. We studied a patient with primary sclerosing cholangitis whose gallbladder was excluded from his extrahepatic bile ducts by stricture formation. He was admitted into hospital because of cholecystitis and cholangitis and required separate drainage tubes into his gallbladder and common hepatic duct. This unique combination of drains afforded the opportunity to examine hepatic bile and gallbladder secretion. We analyzed samples for fluid volume, protein, electrolyte concentrations and biliary lipids. The simultaneous, yet separate, drainage from the gallbladder and the liver had a striking difference. The former was colorless to opalescent; the latter always golden brown. Hepatic bile flow was continuous but gallbladder drainage was variable in volume, intermittent, and occurred only after a meal. The gallbladder fluid had no bilirubin, bile salts, cholesterol, or phospholipids and had the ionic profile of an extracellular fluid. It was alkaline and contained abundant bicarbonate. We have shown that the gallbladder can secrete. In addition, these observations may also have important implications in the pathogenesis and prevention of gallbladder sludge and stones.