The pathogenesis of viral leukoencephalomyelitis of goats was studied in newborn and adult goats using purified, concentrated leukoencephalitis virus. The disease could be transmitted using purified leukoencephalitis virus or tissue suspensions from a goat experimentally infected with leukoencephalitis virus. As early as 1 week following inoculation, goats developed lesions in the brain, joint, and lung. Lesions persisted 8 to 21 months, were not age-dependent, and were inflammatory in character. In the brain they were accompanied by demyelination. Virus could be isolated from experimental goats by cocultivation of peripheral blood leukocytes and by explantation of tissues beginning a week after inoculation and throughout the life of the goat. These studies confirm that leukoencephalitis virus is the etiologic agent of leukoencephalitis-arthritis of goats and produces a persistent infection characterized by demyelinating encephalitis, progressive arthritis, and interstitial pneumonia.