Cerebrospinal lesions of chicks experimentally infected with avian encephalomyelitis (AE) virus were investigated morphologically. Central chromatolysis in motor neurons was mostly reversible, while affected Purkinje's cells revealed necrosis with glial reaction. Direct fluorescent antibody technique revealed various amounts of granular antigen in Purkinje's cells of all chicks showing marked leg paralysis. AE virus particles, 25nm in diameter, were found in crystalline arays in the cytoplasm of the same cells.