A non-protein diet supplemented with vitamins fed to a bile fistula dog caused marked reduction in cholic acid and taurocholic acid formation. A mixture of pure amino acids, essential for growth, promoted taurocholic acid production for a limited period. A mixture of amino acids composed of 2 fractions of a casein digest fortified with dl-methionine and dl-tryptophane, (Merck Vuj-N-ix), also resulted in increased taurocholic acid excretion. A casein digest, Amigen, supported cholic acid production, but there was very low taurocholic acid excretion. Addition of methionine to the Amigen brought about increased taurocholic acid excretion with reduction in the amount of free cholic acid in the bile. A bile fistula animal was maintained for a year in excellent condition and produced bile salt on a non-protein diet supplemented by vitamins, Amigen, and methionine. Unhydrolyzed alcoholic filtrate of bile contained traces of taurine, valine, glutamic acid, and aspartic acid. Acid-hydrolyzed alcoholic filtrate of bile contained large amounts of taurine, and significant amounts of leucine, valine, alanine, glycine, serine, glutamic acid, and aspartic acid.