A hybrid artificial liver (HAL) could be used to treat acute liver failure or to serve as a temporary support until orthotopic liver transplantation is available. Primary human hepatocytes are ideal as a source of hepatic function in a HAL device. However, the worldwide shortage of human livers available for hepatocyte isolation severely limits this form of therapy. A possible alternative is to use a tightly regulated cell line that can be economically grown in culture to have differentiated liver function. In this work, human hepatocytes were immortalized with a retroviral vector SSR#69 expressing the genes of simian virus 40 large T antigen and herpes simplex virus-thymidine kinase. One of the resulting clones, NKNT-3 , showed the gene expression of differentiated liver function and were sensitive to the antiviral agent ganciclovir. When transplanted into the spleen of rats subjected to 90% hepatectomy, NKNT-3 cells prolonged the survival of 90% hepatectomized rats. The cells provide the advantages of unlimited availability, sterility, uniformity, and freedom from pathogens. This work represents a potential novel strategy for resolving the organ shortage that currently limits the use of primary human hepatocytes to develop a HAL.