An epithelial cell line, 3105, with an unusual growth pattern has been derived from the liver of an (NZB x NZW)F1 mouse. When confluent, it forms a monolayer of closely packed cells interspersed with holes that do not fill in during cultivation. By electron microscopy, the line has tight and intermediate junctions as well as desmosomes typical of epithelial cells. It produces several enzymes normally present in liver including hydroxymethylglutaryl-coenzyme A (HMG-CoA) reductase, glucose-6-phosphatase, and alkaline phosphatase; has cytochromes P-450 and b5; and spontaneously release xenotropic but not ecotropic endogenous mouse type C viruses. Inoculation of the cell line into athymic nude mice gives rise to benign cysts in 2-3 months. This mouse epithelial line with hepatocyte characteristics should be helpful to investigators as a cell model of normal liver cell differentiation.