Eight dogs, 14 weeks to 5.5 years of age, had signs of diffuse or multifocal meningoencephalomyelitis. The total white cell counts of the cerebrospinal fluid (CSF) ranged from 11 to 5,550 cells/μl; the percentage of eosinophils ranged from 21% to 98%. The total CSF protein content range was 19 to 1,430 mg/dl. On necropsy, two dogs had granulomatous encephalomyelitis due to protozoan infection. The other six dogs, of which three were Golden Retriever dogs, appeared to have an idiopathic eosinophilic meningoencephalitis; four of these dogs recovered. The significance of eosinophils in CSF and the possible emergence of a new encephalitic syndrome of dogs involving a hypersensitivity to an unknown agent is also discussed.