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. One wk following inoculation, goats developed lesions in the brain, joint and lung. Lesions persisted 8-21 mo., 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 co-cultivation of peripheral blood leukocytes and by explanation of tissues beginning 1 wk after inoculation and throughout the life of the goat. 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.