In hepatic coma as well as diabetic coma severe disturbances occur in the amino acid metabolism. The defect lies in completely different levels which result two different plasma aminograms (PAG). In 24 patients with hepatic encephalopathy stage III-IV (7 patients with acute and 17 with chronic liver failure) the PAG were evaluated. The determination of the plasma amino acids (PAA) was carried out on Multichrom B (Beckmann, Munich). In hepatic coma high concentrations of Met, Tyr, Ala, Lys and Arg are found. The deviations of PAA from normal controls show between acute and chronic hepatic failure no qualitative but only quantitative differences. In diabetic coma the three branches chain AA (Val, Leu and Ile) were elevated upon 3--5 times of normal. Near normal concentrations are found for the AA Thr, Ser, Gly, Ala, Met and the aromatic AA (Phe and Tyr). The quotient between the branched chain and aromatic AA lies for hepatic coma at a mean of 1.18 and by diabetic coma at 7.18 (p less than 0.001). In hepatic coma a correlation exists between the level of the AA-quotient improvement and the decrease with a deterioriation of the metabolic encephalopathy. The high level of the AA-quotient in the patients of diabetic "coma" gives therefore a good explanation for the rare unconscious state of these patients.