Changes of free amino acids in plasma and brain of rats with fulminanthepatic failure were measured with a Beckman 6300 amino acid analyzer.Results indicat-ed that as hepatic encephalopathy developed, concentrations of almost all amino acids inplasma and brain were increased.The levels of most amino acids in brain showed no cor-relation with their changes in the plasma.However,changes of concentrations of theseamino acids in brain that were related to the development of hepatic encephalopathy wereclosely correlated with their concentrations in plasma.Not any correlations between chan-ges of any amino acids in plasma and brain were found in normal control rats.Theseresults suggested that amino acid transport mechanisms appeared to be specific in the blo-cd-brain barrier during fulminant hepatic failure,a phenomenon that could contribute tothe neural disturbance of hepatic encephalopathy.