2'-Nor-2'-deoxyguanosine (2'NDG), a new antiviral agent, conferred protection when given orally or topically to hairless mice after the mice were subjected to orofacial infection with herpes simplex virus type 1. The average severity of orofacial lesions was significantly reduced in mice receiving oral gavage treatments twice daily for 7 days beginning 3 h postinfection. The minimum effective dose of 2'NDG was 0.2 mg/kg per day. A minimum of eight treatments over 4 days resulted in a significant reduction in lesion severity. Topical treatment begun 3 h postinfection and continued four times daily for 3 days resulted in a minimum effective dose of 0.06%. Oral treatment with 2'NDG begun as late as 72 h postinfection or topical treatment begun as late as 48 h postinfection resulted in significantly reduced lesion severity compared with lesion severity among placebo-treated animals. In addition, significant prevention of ganglionic infection occurred when 2'NDG was administered either orally or topically within 24 h after infection.