Increases in serum and tissue bile acid concentrations occur in hepatobiliary disease. In feline patients, the determination of serum bile acid concentrations is a sensitive and specific test for the diagnosis of acquired hepatobiliary disease and congenital portosystemic shunts. Because it is known that high concentrations of bile acids are cytotoxic, it has been speculated that they contribute to the pathological progression of hepatobiliary disorders. Recent evidence suggests the oral administration of the relatively nontoxic bile acid, ursodeoxycholate, can replace more hydrophobic hepatotoxic bile acids in the circulating pool and by doing so ameliorate the harmful effects of the latter. In addition, ursodeoxycholate has choleretic and immunomodulatory actions which may be of benefit in hepatobiliary disorder.