Mice were infected with respiratory syncytial (RS) virus or with recombinant vaccinia viruses (rVV) expressing individual RS virus proteins. rVV-G, rVV-F and, to a lesser extent, rVV-P induced ELISA-binding anti-RS virus antibodies; those induced by rVV-P were non-neutralizing. Different antigens induced helper T cells with distinct cytokine secretion profiles: some released IL-2, and others predominantly IL-4 and 5. Virus-specific cytotoxicity was induced by infection with RS virus, rVV-F or rVV-22K. Different RS virus proteins (given in the same route and form) therefore prime for functionally distinct T-cell activities. These patterns of virus-specific immunity may help explain the pathogenicity of RS virus vaccines, and help in the design of protective, non-pathogenic vaccines in the future.