Several immortalized cell lines were established from the livers of two transgenic rats expressing the simian virus protein large T antigen under the control of the albumin promoter. Hepatocytes from transgenic rats were isolated by a two-step perfusion procedure from a normal- appearing liver and from a liver that contained a single neoplasm. Cells were also isolated from the dissociated liver neoplasm. After 5 weeks in culture, cell colonies were isolated and subcloned as individual cell lines. Electron microscopy revealed that all cell lines had a high nuclear-to-cytoplasmic ratio compared with normal hepatocytes. The cytoplasm contained numerous organelles, including smooth and rough endoplasmic reticulum, Golgi, mitochondria, peroxisomes, and annulate lamellae. However, the lines exhibited a variety of different cell morphologies. All cell lines, including those derived from neoplastic cells, exhibited a similar doubling time of 26 hours and the ability to grow in soft agar. Northern blot analysis revealed that the cell lines differentially expressed hepatocyte markers. Large T antigen was expressed in the cultured cell lines at much higher levels than was observed in transgenic hepatocytes in vivo. This suggests that the viral protein is required to maintain cell viability in culture. In addition, the tumor suppressor proteins, p53 and Rbp105, were detected in all cultured cell lines. In contrast, these same proteins were not detected by Western blot in transgenic hepatocytes in vivo. All cell lines expressed the oncogene c-myc, yet growth factor-dependent and independent growth were observed. The data presented show for the first time the establishment and characterization of a number of cell lines derived from hepatocytes isolated from an alb-SV40 large T-antigen transgenic rat. These cell lines exhibited varied morphological and biochemical hepatocellular characteristics in vitro, suggesting that the expression of the transgene in hepatocytes leads to considerable phenotypic diversity analogous to that seen in hepatocellular carcinomas induced by chemical carcinogenesis.