We report the generation of stable transfectant cell lines by DNA-mediated transfection that overexpress viral and/or cellular oncogenes. Expression of heterologous genes (FBJ- and FBR-v-fos, polyoma large and middle T) was confirmed by Northern hybridization, immunofluorescence and immunoprecipitation. We also describe the isolation of two retinoblastoma cell lines from human tumors. Neuronal and glial markers were used to confirm the origin of these cell lines. Oncogene transfectant and retinoblastoma cell lines will be used to assess Rb expression and the possible role of its gene product in cell proliferation control and neoplasia.