Discriminative and prognostic signs in 14 patients with acute hepatic coma, treated by exchange transfusion and permanent intensive care are described. Five patientssurvived and in none of them was there evolution towards cirrhosis. Nine patients diedduring the therapy, without any temporary clinical improvement. The clinical encephalopathy was initially very similar in both groups. Other parameters were, however, different and might have a prognostic value. The arterial blood ammonia and prothrombinvalue were initially more disturbed and improved only very partially with treatment in thegroup with lethal outcome. The EEG abnormalities were also more pronounced in the latter group; none of the patients with an EEG pattern 4b survived. The histological examination of liver specimens revealed more extensive necrosis with interlobular confluence inthe patients who died.