An animal model of focal herpes simplex encephalitis was used to study several strains of type-1 herpes simplex virus. Rabbits were inoculated in the olfactory bulb by a standardized technique. Virus strains resulting in mortality of greater than 70% produced seizures of 3 types, and all animals that seized became moribund or died. In contrast, a virus strain resulting in a 20% mortality produced no seizures. Administration of 60 mg phenobarbital intramuscularly daily reduced mortality significantly in animals given the epileptogenic viruses. Cultures from temporal and frontal lobes showed viral growth more frequently than did cultures of other brain areas. Microscopic examination of routine and immunoperoxidase-stained brain sections confirmed the focal nature of the infection. Clinical syndromes such as seizures arising from viral brain disease may influence mortality in animal model systems.