This is a phase III blinded study, which will involve approximately 200 patients. For this purpose, acute liver failure will be defined as onset of any mental status alteration and coagulopathy (INR > 1.5) within 26 weeks of onset of a hepatitic illness, with no evidence of underlying chronic liver disease. Eligible patients will be those admitted to study site hospital intensive care units with acute liver failure and who can be evaluated and started on treatment within the first 24 hours of hospitalization or those who evolve to altered mentation if already in the hospital. All subjects will be between 18 and 70 years. Patients transferred from referring hospitals to a study site may be considered for enrollment, provided that no other specific treatment protocol has begun, and that no liver support device (bioartificial liver (BAL), extracorporeal liver assist device (ELAD), transgenic pig perfusion) has been used or is contemplated. Use of fresh frozen plasma infusions will not disqualify patients from participation.