Serum bile acid classes have been studied in 15 patients with primary biliary cirrhosis in five patients with cholestasis, and in five patients who had cirrhosis without cholestatic features. Conjugated monohydroxy bile acids (12-35% serum total bile acids) were found in eight of 11 sera from patients with primary biliary cirrhosis, in sera from four patients with cholestasis but not in any of the five patients with cirrhosis. The glycine conjugates/taurine conjugates (G/T) ratio in eight of 11 patients with primary biliary cirrhosis and two of four patients with cholestasis was <1.0. Bile acid concentrations in seven patients with primary biliary cirrhosis were measured before and during cholestyramine therapy. Decreases in serum total bile acid concentrations were observed which were accompanied by small increases in the trihydroxy/dihydroxy ratio and also in the G/T ratio in six of the seven patients. No association was found between the concentration of any particular conjugated or free bile acid and the presence or absence of pruritus.