Publisher Summary Most of adenoviruses produce subclinical infections, with occasional evidence of upper respiratory disease; however, the canine and avian adenoviruses are associated with a variety of important diseases, including hepatitis. The classification of these virusesis based primarily on antigenic relationships. The restriction endonuclease fragment patterns of the viral DNA are useful for the detailed comparisons of strains. Shared antigenic determinants associated with the inner part of the hexamers define two genera: Mastadenovirus, the mammalian adenoviruses, and Aviadenovirus, the avian adenoviruses. There are also genus-specific antigenic determinants on the pentamer. Adenoviruses apparently enter the cell by direct translocation across the plasma membrane. The pentons are removed in the cytoplasm and the core migrates to the nucleus. In the nucleus, the genome is transcribed according to a complex program.