The pathogenesis of herpes simplex virus (HSV) types 1 and 2 was compared after inoculation of mice by different routes. Intravaginal inoculation of HSV-1 and HSV-2 produced a local infection, with virus recovery from the vagina through 5 days. Virus was recovered from the spinal cords 4 to 5 days after inoculation but not from liver, kidney, lung, spleen, or blood. Intravenous or intraperitoneal inoculation of HSV-2 produced a focal necrotic hepatitis similar to that described previously (S. C. Mogenson, B. Teisner, and H.K. Andersen, 1974). The viral etiology of the liver lesions was confirmed by virus isolation (through 4 days) and electron microscopy. No evidence of infection of the kidney, lung, blood, or spleen was observed, although virus was isolated from spinal cord homogenates 7 days after inoculation. HSV-1 inoculation by the intraperitoneal or intravenous route resulted in virus isolation from the kidney during the 7-day harvest period, without producing overt pathological changes. Virus was isolated from spinal cord homogenates 2 to 3 days after HSV-1 inoculation but not from homogenates prepared from spleen, lung, or blood. Increases in serum transaminase activity were observed after systemic (intravenous) inoculation of HSV-2 but not after HSV-1 inoculation.