Neuromyelitis of cyanocobalamin deficiency (gruop 1) post vaccination myelopathy (group 2), multiple sclerosis and neuromyelitis optica (group 3) are studied comparatively as to the respective cerebrospinal fluid changes on cytology, proteins and gamma globulins. Changes were found to be more intense and frequent in the last two groups. Local immunecompetent phenomena are considered in the interpretation of findings and related to modifications that may be induced in myelin macromolecules by factors of diverse order which may be involved in demyelination in each onde of the thre groups.