The limited donor organ supply has led to several bridging techniques to sustain patients with acute and subacute liver failure. We report here the prospective, controlled trial of transplanted isolated fresh and cryopreserved human hepatocytes as a bridge to orthotopic liver transplantation. Five hepatocyte transplant recipients with grade IV encephalopathy and multisystem organ failure and four patients of equal illness severity due to liver failure were studied. Medical therapy resulted in a significant (P<0.05), but not normal, fall in blood ammonia, and a significant (P<0.02) resolving biochemical marker of liver injury that did not improve cardiovascular or cerebral stability; this lead to death within 3 days in all control patients. The five hepatocyte-treated patients maintained normal cerebral perfusion and cardiac stability, with withdrawal of medical support for 2 to 10 days before orthotopic liver transplantation. Biochemical evidence of liver injury improved significantly (P=0.004) and blood ammonia levels decreased significantly (P=0.0005) to normal levels in the hepatocyte-treated patients. Three of five patients who successfully bridged to whole liver allograft transplant are alive, home, and normal with more than 20 months of follow-up. No infections or embolic or pulmonary complications resulted from intra-arterial splenic hepatocyte infusion. Specific antiprotease production in a patients with genetically deficient alpha-1-antitrypsin disease, and immunohistochemical and electron microscopic evidence of splenic "hepatization" are presented as evidence of the viability of hepatocyte splenic seeding. In conclusion, splenic transplantation of differentiated adult hepatocytes can control hyper-ammonemia, correct genetic defects in liver function, and bridge life to orthotopic liver transplantation in human liver failure.