Vesicular stomatitis virus (VSV) Indiana was a gift from Amiya K. Banerjee, Lerner Research Institute, Cleveland, Ohio. For intranasal infections, between 4610 2 and 4610 6 pfu of VSV in 35 ml of endotoxin-free PBS were inhaled by isofluorane-anesthetized 8-12 week-old mice, with PBS-only as control. For intracranial infections, 10 pfu of VSV in 30 ml of endotoxin-free PBS were injected into the brains of 6-7 week-old mice, with PBSonly as control. Thereafter, mice were monitored daily (twice daily after i.c. injection) for weight loss and symptoms of disease. Encephalomyocarditis virus (EMCV) K strain was a gift from Robert H. Silverman, Lerner Research Institute, Cleveland, Ohio. For intraperitoneal infections, between 25 and 5610 2 pfu of EMCV in 500 ml of PBS were injected into the peritoneal cavity of mice. Mice were monitored daily for weight loss and symptoms of disease.