The role of CD8+ T cells in resistance to herpes simplex virus (HSV) was examined. After cutaneous inoculation, HSV spreads to the peripheral nervous system (PNS) where it replicates in ganglionic neurons. In normal mice, replication of virus in the PNS was rapidly terminated and evidence of neuronal destruction, assessed by a quantitative histological assay, was sparse. Clearance of infectious virus was impaired, and a strikingly high proportion of ganglionic neurons was killed, in mice treated with an antibody that depleted them of CD8+ T cells. These results suggest that CD8+ T cells play an important role in maintaining the integrity of the sensory nervous system during primary infection with HSV. Therefore, viral epitopes recognized by CD8+ T cells and restricting class I major histocompatibility complex genes are, in principle, implicated as interacting genetic determinants of neurovirulence.