The chemical composition of biliary calculi from 25 Singapore patients operated upon over a three month period was determined by a microanalytical technique and equilibrium swelling tests. Twelve patients had biliary calculi confined to the gallbladder and the main component of six calculi was cholesterol. In the other 6 patients, the dark brown to black pigment calculi contained bilirubin and calcium and a small quantity of cholesterol, but the chief component was an insoluble pigment with the swelling characteristics of a bilirubin polymer. These cholesterol and pigment calculi have similarities in composition to gallstones of Western patients. In 13 patients with cholangitis, the brown, soft pigment calculi found in the dilated bile ducts (and also concurrently in the gallbladder in 5 patients) had bilirubin as the main component. Fatty acid was frequently present. The insoluble pigment component was considerably less but the lower swelling ratio suggested more cross linkage compared with black gallbladder stones. Differences in chemical composition between pigment gallbladder and bile duct calculi support the concept that Western type cholelithiasis and Oriental cholangitis occur as separate disease entities in Singapore patients.