1. Neutralizing antibody to equine encephalomyelitis virus was found in the spinal fluid of rabbits sufficiently vaccinated with active or formalin-inactivated virus. Antibody was specific for the Western or for the Eastern virus.
2. Neutralizing capacity of spinal fluid was equivalent to that of a 1/300 dilution of serum of the same animal, and was of the same order of magnitude as that of perfused brain of a vaccinated animal.
3. Vaccinated rabbits which showed antibody in the spinal fluid resisted intracerebral or intracisternal injection of active virus. This immunity was specific, i.e., there was no cross-reaction between the Eastern and Western virus after vaccination with formalin-inactivated virus. On the other hand, lack of antibody in the spinal fluid, even when antibody was demonstrable in the undiluted serum, was associated with lack of cerebral resistance.
