We examined cytolytic cells that lyse pseudorabies virus (PRV)-infected cells in pigs. In vitro stimulation of peripheral blood mononuclear cells from PRV-immune pigs with live PRV generated cells that lysed PRV-infected immortalized B cells. Several lines of evidence indicated a major contribution of non-major histocompatibility complex (MHC)-restricted cytolytic cells, which displayed characteristics of natural killer (NK) or lymphokine-activated killer cells: cytolysis was non-MHC-restricted, depended on CD2+CD4-CD8bright- (or CD2+CD4-CD8dull+) cells, was strongly augmented by in vitro antigenic stimulation and was not limited to virus-infected cells, i.e. the NK cell-susceptible target cell line K562 was also lysed. Cytolytic cells were also generated by in vitro antigenic stimulation with UV-inactivated PRV. Target cells transfected with and stably expressing PRV gB or gC were lysed to the same degree as PRV-infected target cells.