An experimental central nervous system (CNS) disease that bears some similarity to human multiple sclerosis and that is associated with infection by measles virus has been induced in hamsters. This disease has been described previously (Carrigan and Johnson: Proceedings of the National Academy of Sciences 77:4297-4300, 1980). At that time, it was believed that the disease was restricted to the spinal cords of affected animals. The present work demonstrates that the disease can also affect the brain, describes in more complete detail the types of clinical disease that occur, illustrates the histopathological changes found in diseased CNS tissues, and documents more accurately the incidence of the disease in the virally infected animals. In summary, the disease, which has now been termed chronic, relapsing encephalomyelitis (CRE) is associated with neonatal CNS infection of hamsters with a particular strain of measles virus. CRE occurs in approximately 12% of animals that survive the acute viral infection, and of these affected animals about half develop detectable clinical signs of neurological disease. The balance of the animals have subclinical disease detectable only by histopathologic changes within the CNS. These lesions are composed of varying degrees of demyelination, necrosis, mononuclear cell inflammation, and gliosis.