The requirement for specific T cell subsets in the in vitro generation of human influenza virus-immune cytotoxic T lymphocyte (CTL) responses was investigated. Peripheral blood T cell populations were identified by and selected for their reactivity with the monoclonal antibodies OKT3, OKT4, and OKT8. Influenza virus-immune CTL effectors are OKT3+, OKT4-, and OKT8+. Analysis of CTL precursors demonstrates that: 1) influenza-immune CTL precursors are OKT3+, OKT4-, and OKT8+; 2) CTL precursors require radioresistant OKT3+ helper T cells in order to generate strong cytotoxic responses; and 3) helper T cells can be obtained from either the OKT4+ or OKT4- populations, but more potent help was generated by the OKT4+ subset. The demonstration of a helper T cell requirement for the generation of influenza virus-immune CTL suggests that helper T cells may be involved in the previously documented HLA-linked Ir gene control of influenza-immune CTL responsiveness.