The immunology of herpes simplex infections has been reviewed, particularly in relation to potential herpes simplex virus (HSV) vaccines, and to the association between HSV and cervical cancer. Relevant data from humans, experimental animals, and in vitro systems implicate both specific immune mechanisms and nonspecific factors in the course of HSV infections. There appear to be complex interactions between the various populations of mononuclear cells, marcrophages, and lymphokines or other humoral factors. It is not yet possible, however, to pinpoint the crucial factors determining the different manifestations of the viral infection (primary infection, endogenous recurrence, or exogenous reinfection) in the various human hosts, although genetic factors may be important. While numerous animal models of HSV infection are available for the evaluation of HSV vaccines, models of HSV-induced cervical cancer require further exploration.