The influence of the taurine-containing amino acid mixture Trophamine on the pattern of bile acid conjugation was examined in the isolated perfused rat liver using cholic acid as the bile acid substrate. In all experiments, greater than 97% of the cholic acid appearing in bile was conjugated with taurine or glycine. The pattern of taurine and glycine bile acid conjugation, however, was dependent on the availability of taurine in the perfusate medium. Thus, in the absence of Trophamine infusion, the percentage of cholic acid conjugated with taurine (ie, taurocholate) declined throughout the course of the cholic acid infusion. Trophamine infusion increased the ratio of biliary taurocholate/glycocholate by 4.5-fold over that observed in the absence of the amino acid infusion. Increasing the amount of taurine in Trophamine by 2- or 5-fold resulted in a 1.8- and 4.3-fold increase, respectively, in the taurocholate/glycocholate ratio over that observed during the Trophamine infusion. Infusion of taurine alone, at an equimolar concentration of taurine as that in Trophamine, resulted in a similar taurocholate/glycocholate ratio as that observed during the Trophamine infusion. These data indicate that taurine availability, even in the presence of high concentrations of glycine and other amino acids in Trophamine, appears to be the most important factor in determining the pattern of bile acid conjugation in the isolated perfused rat liver.