Mice lethally infected with street rabies virus failed to develop cytotoxic T cells specific for rabies virus-infected target cells, whereas high levels of cell-mediated cytotoxicity (CMC) were generated after nonfatal infection with the attenuated high egg passage (HEP) or ERA rabies virus strains. Furthermore concurrent infection with street, but not with HEP, rabies virus suppresses development of a primary (but not a secondary) CMC response specific for influenza virus. No cross-reactivity is found between effector T-cell populations from mice immunized with HEP or with influenza virus. It thus appears that street rabies virus, which is not known to replicate in the cells of immune system, induces some general defect in the primary CMC lymphocyte response, though restimulation of memory T-cell populations is unimpaired and there is no defect in antibody formation. Development of fatal rabies may reflect the operation of this selective immunosuppressive mechanism.