The pathogenesis of viral and mycoplasmal infections is probably similar, but pathologic findings vary, depending on the etiologic agent. In the absence of inclusion bodies in epithelial cells, definitive diagnosis of viral pneumonia depends on isolation of the virus. Viral pneumonias are more insidious in onset than bacterial types. In the early stages, physical findings may be minimal. Complications include those associated with viremia or bacterial superinfection. Culture of a throat swab is suitable for isolation of almost all respiratory viruses except respiratory syncytial virus, which requires special techniques. Antibody studies are also of great value. The major effort in controlling viral illness has been prevention of infection by vaccination. Treatment at present is symptomatic.