Herpes simplex virus (HSV)-specific T cells are essential to control and resolve genital herpes (GH). To investigate the potential involvement of gamma delta T cells in GH, T cells were recovered and expanded, by mitogenic stimulation, to T cell lines from the genital lesions of 17 patients with GH and 5 control subjects who had other diseases. Relatively high numbers of gamma delta T cells--predominantly, V gamma 9V delta 2 T cells--were detected only in the T cell lines of the patients with GH. Intralesional V gamma 9V delta 2 T cell clones did not recognize HSV-infected cells, but they showed reactivity to isopentenyl pyrophosphate and Daudi cells. The T cell clones secreted interferon- gamma, tumor necrosis factor- alpha, interleukin (IL)-8, macrophage inflammatory protein-1 alpha, and RANTES (regulated on activation, normally T cell expressed or secreted), but they secreted no or limited IL-4. The results of the present study suggest the infiltration and putative involvement of isopentenyl pyrophosphate-reactive V gamma 9V delta 2 T helper 1-like cells in individuals with GH.