Based on the assumption that middle molecules that induce hepatic coma occur in the plasma of patients with fulminant hepatic failure (FHF), the authors have developed a hemodiafiltration (HDF) method using a large-pore poly(methylmethacrylate) (PMMA) membrane that allows proteins to pass through. PMMA HDF resulted in complete recovery of deep coma and longterm survival in a patient with severe FHF. Although a large-scale controlled trial is needed, PMMA HDF is believed to be promising as a future artificial liver support.