Extracorporeal liver perfusion (ECLP) using xenogeneic whole liver has been used as a liver assist device to treat liver failure in many institutes during the 1960s and 1970s, resulting in transient improvements of clinical manifestation. Nevertheless, this method has not shown satisfactory patient outcome, due to its limited duration, caused by xenogeneic humoral injury to the graft liver. Recently, shortage of donor organs has become a serious problem in liver transplantation. The liver assist device is necessary to treat patients with end-stage liver diseases, especially fulminant liver failure, until liver transplantation can be undertaken. Based on advancements in xenotransplantation research, xenogeneic ECLP as a liver assist device has been reevaluated at some institutes.In our previous study, we perfused pig liver with human blood for up to 9 hours under nearly physiologic conditions with continuous administration of prostaglandin E 1 into the portal vein. In the latest study, additional treatment by administration of soluble complement receptor type 1 dramatically reduced humoral injury of the xenoperfused liver.In this study, we evaluated the efficacy of a xenogeneic ECLP as a liver assist device using PGE 1 and sCR1 on liver failure in the animal model.