We studied the effects of the type of dietary fat and of ursodeoxycholic acid, an exogenous bile acid added to the diet, on bile physiology in rats with 50% resection of the distal small intestine. The amount of fat was the same (4%) in all diets assayed, which differed only in the type of fat, (olive oil in diet A, and 1/3 medium-chain triglycerides, 1/3 sunflower oil and 1/3 olive oil in diet B). The removal of 50% of the distal small intestine raised the de novo hepatic synthesis of bile acids with respect to controls, regardless of whether diet A or diet B was given. The addition to diet B of ursodeoxycholic acid decreased bile flow and osmotic activity of bile acid in resected rats and raised bile acid-independent bile flow in comparison to resected rats given diet B without ursodeoxycholic acid.