Abstract: The present invention provides methods for detecting the oncogenic state of cells by detecting the complex formation between the E2F transcription factor and the retinoblastoma (Rb) protein. A first embodiment is a diagnostic assay for detecting the state of Rb function of cells by collecting a cell sample and then detecting free E2F in the cell sample, the presence of free E2F indicating the loss of Rb function of the cells. A second embodiment is a bioassay for screening test compounds for the ability to inhibit the oncogenic state of cells. The bioassay comprises contacting a test compound to a cell capable of producing a complex of the Rb protein and the E2F transcription factor, the cell containing a virus expressing a viral oncoprotein capable of disrupting the complex, and then detecting the appearance of the E2F-Rb complex in the cells, the presence of the E2F-Rb complex indicating the oncogenic state of said cells.