Although multiple sclerosis is considered to be an autoimmune disease in the CNS, the immune responses that take place in the CNS and lymphoid organs remain to be elucidated. Here, we have successfully induced various subtypes of experimental autoimmune encephalitis (EAE) in LEW.1AV1 rats carrying RT1(av1) on the Lewis background genes by immunization with recombinant rat myelin oligodendrocyte glycoprotein (MOG) in various solutions with adjuvants. The purpose of the present study was to analyse in more detail the clinical and immunopathological features of MOG-induced EAE in LEW.1AV1 rats. Immunization with high doses of soluble MOG with pertussis toxin induced acute, frequently fatal EAE, whereas medium doses of partially aggregated MOG without pertussis toxin produced relapsing and remitting EAE. Secondary progressive EAE was induced in some rats by immunization with the immunization protocol having an intermediate nature between the above two. The optic nerve (approximately 60% of the immunized rats) and spinal cord (100%) were frequently involved and detectable both clinically and pathologically, while there was no lesion in the cerebrum. Histological examination revealed that, despite variety in the clinical subtypes, progression of the pathological processes was strikingly uniform, i.e. initial inflammation with minimal demyelination followed by predominant demyelination with minimal lymphocyte infiltration. These findings suggest that the lesion during the later stage is maintained by humoral factors. Taken together, this experimental system can serve as a model of neuromyelitis optica. Further analysis will provide useful information to elucidate the pathogenesis and to develop immunotherapy for neuromyelitis optica and multiple sclerosis.