We postulated that coadministration of cholylsarcosine with ursodeoxycholic acid might provide additional benefit to primary biliary cirrhosis patients with an incomplete response to ursodeoxycholic acid. Our aim was to test the tolerability and the effect of adjuvant cholylsarcosine on liver tests and plasma cholesterol in primary biliary cirrhosis patients receiving ursodeoxycholic acid. Four primary biliary cirrhosis patients, who, despite more than a year of ursodeoxycholic acid therapy, had one or more liver tests persistently equal to or greater than twice the upper limit of normal, received cholylsarcosine (12-15 mg/kg/day) in addition to ursodeoxycholic acid (13-15 mg/kg/day) for six weeks in an open label study. Values of liver tests and plasma cholesterol, determined every two weeks, remained unchanged. One patient discontinued cholylsarcosine at week 4 because of new-onset pruritus. Analysis of duodenal bile acids in one patient showed 52% enrichment in cholylsarcosine and hydrophilic bile acids constituted 87% of total bile acids. It is concluded that the addition of cholylsarcosine to ursodeoxycholic acid did not influence liver tests in four primary biliary cirrhosis patients who had not responded completely to ursodeoxycholic acid alone. Cholylsarcosine was absorbed and became a dominant biliary bile acid; its administration was associated with increased pruritus.