This study was carried out to investigate the metabolic alteration of plasma and CSF amino acids in patients with liver cirrhosis only and liver cirrhosis with hepatic encephalopathy. Plasma amino acids were measured in 20 cases of liver cirrhosis only, 17 cases of patients with hepatic encephalopathy and 20 cases of normal person as a control. Among above groups of patients, CSF amino acid concentrations were measured in 15 cases of liver cirrhosis only, 17 cases of patients with hepatic ence-phalopathy and 15 cases of normal person. The plasma amino acid concentrations were determined by high performance liquid chromatography. The results were as follow: The plasma concentrations of branched chain amino acids (valine, leucine, isoleucine) were lower in cirrhotic patients and patients with hepatic encephalopathy (p<0.05) than control group and more decreased in patients with hepatic encephalopathy than cirrhotic patients. The plasma concentrations of phenylalanine in aromatic amino acids increased in hepatic encephalopathy (p<0.05), but tyrosine increased in both group of patients (p<0.05). 1n the study of CSF, there were no significant changes in branched chain amino acid concentrations, but in aromatic amino acid concentrations (phenylalanine, tyrosine) increased (p<0.05). In hepatic encephalopathy compare to liver cirrhosis only, phenylalanine concentration was higher (p<0.05) in CSF. The molar ratio between branched chain amino acids and aromatic amino acids (Val.+Leu.+Isoleu./Phen.+Tyr,) of plasma and CSF were lower in both groups of patients than control. In hepatic encephalopathy com-pare to liver cirrhosis only, the molar ratio was lower in hepatic encephalopthy.