Acute hepatic failure was induced in rats with intraperitoneal administration of D-galactosamine.Serum and tissue amino acid profiles of the animals were studied. Except for arginine, serum levels of all amino acids were elevated. This is in variance with the findings of Fischer and other investigators. In their studies, the decreased levels of BCAA could be related to the administration of dextrose. In our study, the serum BCAA/AAA ratio was decreased and it was correlated negatively with the dosage of D-galactosamine (r =-0.789). Amino acid profiles in the liver,kidney and muscles were significantly altered. The chracteristics of the changes indicated that enhanced proteolysis of tissue proteins was the major factor accounting for the elevation of serum amino acid levels. Hepatic coma might be related to the increase of aromatic amino acids in the brain. It is usually difficult for glycine, cystine, asparagine and threonine to penetrate the blood-brain-barrier. Elevation of their levels in the brain might be a consequence of increased permeability of the blood-brain-barrier. Further studies are needed to clarify the role of GABA in hepatic coma.