The authors describe a slight but significant increase in the serum levels of indirect-reacting bilirubin in gallstone patients after 3 and 6 mo of treatment with chenodeoxycholic acid. A return to pretreatment values was noted at 9 mo. The mechanism of this abnormality remains unclear. Two explanations are theoretically possible: a subclinical hemolysis or a modification of the hepatic transport and/or the conjugation of bilirubin.