A nonfatal case of herpes B virus encephalomyelitis is presented. The patient is an eminent virologist whose last direct contact with monkeys was 10 years before he became ill. His illness began with a zoster-like lesion of the trigeminal nerve, which suggests reactivation of a latent infection, since he had had no recent exposure to monkeys. The diagnosis of B virus infection was made by isolation of the virus from a skin scraping; it was confirmed serologically. Treatment with prednisone, gamma globulin, and cytosine arabinoside did not seem to affect his course. His survival was primarily owing to intensive supportive therapy.