The bile acids have important physiologic functions including stimulation of bile flow, solubilization of cholesterol in bile and the promotion of efficient intestinal digestion and absorption of lipids.  Bile acids are synthesized in the liver and conjugation with amino acid is the predominate pathway for bile acid modification.  Although sulfation of bile acids is a minor pathway, it is important under certain circumstances.  The sulfation of bile acids is a protective mechanism for the liver whereby the bile acids are converted to their less toxic and more water soluble sulfates.  Bile acid sulfation may be significant in protecting the newborn from intrahepatic accumulation of bile acids, during chenodeoxycholate administration for dissolution of cholesterol gallstones, and by providing a means of urinary excretion of bile acids during cholestasis.  Fundamental to the understanding of bile acid sulfation is determining the number and specificity of liver bile acid sulfotransferase enzyme(s).  The biological parameters that regulate liver bile acid sulfotransferase activity include diet, bile acid administration, bile acid depletion, and fasting will be determined.