Captive baboons of three age groups were experimentally infected with Herpesvirus SA 8-strain 0430. Intravenous inoculation of the virus induced minor, transient, interstitial pneumonia of a nonspecific type in newborn baboons. Intratracheal inoculation, in contrast, invariably produced multifocal or diffuse necrotizing inclusion body bronchopneumonia within two days in newborn, two months and one year old baboons. Differences in the outcome of the experimental intratracheal infections were noticed, depending on the animals age. All the newborns either died from the extensive pulmonary damage or had to be sacrificed because of serious illness. Older animals, in contrast, survived the initial impact with only minor clinical symptoms and repair of the necrotic and inflammatory lesions. The healing stages were characterized by interstitial fibrosis and transient tumorlike bronchial and bronchiolar epithelial proliferations, which lasted for approximately two months. Intranuclear inclusion bodies in ganglionic cells, ganglioneuritis and neuritis in different parts of the pulmonary plexus in intratracheally infected animals suggested the viral invasion of the pulmonary autonomous nervous system.