Exploratory experiments indicate that media containing lipids, phosphoethanolamine, epidermal growth factor, insulin, cholera toxin, bovine pituitary extract, chemically denatured serum, and triiodothyronine will support replicative cultures of normal liver epithelial cells obtained from adult Rhesus monkey and human donors. In addition, we have extended the culture population doubling potential of the human liver epithelial cells by their transfection with a plasmid containing the SV40 virus T-antigen gene. The T-antigen gene-containing cells continued to express albumin through 40 population doublings. Finally, results of preliminary experiments suggest that it may be possible to induce human liver epithelial cells to undergo differentiation to hepatocyte-like cells either by injecting them into the spleen of an athymic nude mouse or by incorporating them into a collagen "tissue equivalent" matrix.