• Clinical and neuropathological observations in chronic, relapsing experimental allergic encephalomyelitis (EAE) are reported and compared with data available for multiple sclerosis (MS). clinical, relapsing EAE was found in 95 of 119 of the strain 13 and 22 of 57 of the Hartley guinea pigs immunized. Examination of the brains and spinal cords of the guinea pigs showed a high incidence of macroscopically visible, demyelinated plaques. The topographic distribution of lesions resembled a pattern similar to that described in MS. Microscopic features of the lesions consisted of perivenous inflammation, primary demyelination, oligodendrocyte loss, and reactive gliosis. It is concluded that, with the exception of minor differences, the clinical and pathological alterations in chronic, relapsing EAE closely resemble those found in MS.