Recurrence rates of genital infections are significantly higher for heφes simplex virus (HSV) type 2 than HSV type 1. Reasons for this difference are not known. In this report, multiple strains of HSV-1 and HSV-2 were evaluated in the guinea-pig model. HSV-2 strains showed significantly higher genital lesion recurrence than HSV-1, including HSV-1 McKrae strain which is highly recurrent in ocular infections. HSV-2 strains were also associated with more frequent asymptomatic vaginal virus shedding. Further study showed that HSV-1 strains replicated as well as HSV-2 in both the genital tract and the nervous system during acute infection. In addition, no difference was detected between HSV-1 and HSV-2 in nervous system latency. Thus, a number of possible explanations for the observed difference in genital heφes recurrence rates were examined and exclude