Epidemiological studies suggest that multiple sclerosis (MS) might be triggered by an infectious agent. Uveitis has been observed in a small percentage of MS patients. Dogs with canine distemper encephalomyelitis, another demyelinating disease of the central nervous system, have an anterior uveitis which is usually mild and asymptomatic, and dogs with persistent CNS infection and chronic distemper encephalomyelitis harbour virus persistently in the uvea. These observations in dogs suggest that pathological and virological studies of the uveitis associated with MS would be worth while.