Relative concentrations of conjugated and sulfated bile acids in duodenal bile were measured in 5 patients before and during treatment with 0.50-0.75 g of chenodeoxycholic acid per day for 3-4 months. Lithocholic acid constituted 0.8-3.3% (mean 1.8%) of total conjugated and sulfated bile acids before and 0-5.4% (mean 2.6%) during treatment. Lithocholic acid was the predominant bile acid in the sulfate fraction in three patients and chenodeoxycholic acid in two. Sulfated bile acids constituted less than 1% of total bile acids and did not increase during treatment. Ursodeoxycholic acid, the other major metabolite of chenodeoxycholic acid, was found in higher amounts during therapy. The unsaturated bile acid 3beta-hydroxy-delta5-cholenic acid, which was found exclusively as its sulfate ester, showed a slight fall. The average G/T conjugation ratio rose from 2.2 to 4.5.