The requirement for interferon-gamma (IFN gamma) in resolution of an HSV-2 vaginal infection and the cellular sources of this cytokine in the vaginal mucosa were assessed. IFN gamma levels in vaginal secretions peaked on Days 2 and 5 following HSV-2 inoculation. Natural killer (NK) cell depletion greatly diminished the early production of IFN gamma but had no significant effect on the rate of virus clearance. CD4+ T cells were primarily responsible for the second peak of IFN gamma levels and neutralization of this IFN gamma beginning 3 days after virus inoculation delayed, but did not prevent, virus clearance from the vagina. HSV-2 persisted in mice depleted of both CD4+ and CD8+ T cells while clearance was delayed in CD4+, but not CD8+ T cell-depleted mice, demonstrating the T cell dependence and predominant role of CD4+ T cells in resolution of the infection. Together, these data suggest that IFN gamma is not essential for virus clearance but plays an important role in enhancing T cell-mediated clearance mechanisms. The implication of these results is that IFN gamma produced locally in the genital tract enhances virus clearance and may ultimately be important for reducing the amount of virus available to infect sensory ganglia.