This brief review paper deals mainly with oncogenic DNA viruses originally isolated from human patients, i.e., human adenoviruses and human papova JC viruses. Human adenovirus type 12 was first isolated in 1953 in cell cultures derived from the adenoids of infected children. Since then, 32 antigenic types of human adenovirus have been identified. At least eight serotypes (12, 18, 31, 3, 7, 14, 16, and 21) are now known to be capable of producing tumors in newborn rodents. A direct causal relationship between a human adenovirus and malignant transformations in target cells (sensory neuronal precursors) has been definitely established by the development of a medullo-epitheliomatous neoplasm in the brain and spinal cord of an outbred strain of CD rats at as high an incidence as 90%. Intraocular inoculation of adenovirus in newborn rats within one week also has produced typical retinoblastomatous neoplasms. The remarkably uniform histopathologic appearance of all these malignancies in nervous tissue can be attributed to a primitive neuro-epitheliomatous neoplasm derived from sensory microneuron precursors that densely populate both the ventricular zone and the premature sensory retina at the point of virus inoculation. All of these brain and retinal tumors appear to share a common tumor phenotype, as all tumor cells contain cilia with the same morphology (a 9+0 pattern of doublets associated with a pair of centrioles). The production of adenovirus tumor-specific neoantigen (T), an earmark of the viral genome, can be regularly demonstrated by the immunofluorescein microscopic procedure. All transformed cells within both the ventricular zone and the retinal ganglion cell anlage thus appear to continue the production of (T) antigens. These findings lead us to assume that the target cell determinants in adenovirus tumorigenesis may reside in differentiating microneuron precursors ordained for the sensory neuronal complex.