Of the almost 100 different serotypes of adenoviruses, 49 are known to affect humans. These viruses are naked and icosahedral and possess double-stranded DNA. Replication and assembly occur in the nucleus, and virions are released by cell destruction. All aden-oviruses share a common group-specific, complement-fixing antigen associated with the hexon component of the viral capsid. Adenoviruses are characterized by their ubiquity and persistence in host tissues for periods ranging from a few days to several years. Their abil-ity to produce infection without disease is illustrated by the frequent recovery of virus from tonsils or adenoids removed from healthy children (the group name is derived from its discovery in 1953 as a latent agent in many adenoid tissue specimens) and by prolonged intermittent shedding of virus from the pharynx and intestinal tract after initial infection.