The biliary bile acid conjugation patterns were determined by high-performance liquid chromatography in five subjects after 6 months of 500 mg per day of free ursodeoxycholic acid feeding. Prior to bile acid therapy, approximately 35% of the biliary bile acids were conjugated with taurine and approximately 65% were glycine conjugated, and ursodeoxycholic acid was either absent or, when present, accounted for less than 5% as the glycine conjugate. After 6 months, ursodeoxycholic acid became the major biliary bile acid and approximately 90% of it was present as the glycine conjugate and approximately 10% as the taurine conjugate. In another experiment, in seven patients, 1 gm per day of sodium tauroursodeoxycholate (equivalent to approximately 750 mg per day of free ursodeoxycholic acid and approximately 250 mg per day of taurine) was administered for 10 days. The proportion of tauroursodeoxycholic acid rose to 41% of the total biliary ursodeoxycholic acid but 59% still remained conjugated with glycine. When three patients were fed 1.5 gm per day of taurine together with 750 mg per day of free ursodeoxycholic acid for 10 days, the taurine conjugation of ursodeoxycholic acid and other bile acids increased to 29 to 40%. These studies show that the administration of free ursodeoxycholic acid results in the increased formation of glycour-sodeoxycholic acid while the administration of 1 gm per day of tauroursodeoxycholic acid or 1.5 gm per day of taurine together with 750 mg per day of free ursodeoxycholic acid increases the excretion of tauroursodeoxycholic acid in the bile only to about 40% of the total biliary ursodeoxycholic acid. Thus, the taurine of tauroursodeoxycholic acid is partially lost during its enterohepatic circulation while the free taurine during taurine supplementation is only partially available for conjugation.