In order to study the mechanism of the imbalance of amino acid metabolism during hepatic failure, a stable isotope tracer method for observing simultaneously the metabolic kinetics of several amino acids has been established. 15N-L-Ala, (2, 3-D3)-Leu and (2, 3-D3) - Phe were chosen as nonessential, branched chain and aromatic amino acids. A. single iv injection of 40 mg 15N-Ala, 20 mg deuterated Leu and 20 mg deuterated Phe was given to each human subject. Blood samples were taken just before and at different times (up to 60 rain) after the injection. Total free amino acids were isolated from the plasma with a small dowex 50 x 8 column and converted to trifluoroacetyl derivatives. Their abundances were then analyzed with a GC-MS system and typical double exponential time course curves were found for all the three labelled amino acids. A two-pool model was designed and applied for compartmental analysis.Significant changes were found in the kinetic parameters of Phe and Leu in patients with fulminant hep In order to study the mechanism of the imbalance of amino acid metabolism during hepatic failure, a stable isotope tracer method for observing simultaneously the metabolic kinetics of several amino acids has been established. 15N-L-Ala, (2,3-D3) - A. single iv injection of 40 mg 15N-Ala, 20 mg deuterated Leu and 20 mg deuterated Phe were given to each human subject (Leu and (2, 3-D3) - Phe were chosen as nonessential, Total free amino acids were isolated from the plasma with a small dowx 50 x 8 column and converted to trifluoroacetyl derivatives. Their abundances were then analyzed with a GC-MS system and typical double exponential time course curves were found for all the three labeled amino acids. A two-pool model was designed and applied for compartmental analysis. Identification of were found in the kinetic parameters of Phe and Leu in patients with fulminant hep