The immune response to HIV in infected humans leads to the production of HIV-specific cytotoxic T lymphocytes (CTL) which circulate in high frequencies. The presence of these CTL and their eventual protective activities have been studied by various laboratories, and correlations have been made with certain immunopathological manifestations of HIV infections. It seems probable that HIV-immune CTL participate in the induction of certain disorders by initiating inflammatory reactions in the lungs, central nervous system and lymph nodes. Various virus antigens recognized by HIV-immune CTL on the surface of the infected cell have been identified, and molecular definition of the epitopes recognized is well under way. Likewise, numerous HLA transplantation antigens that regulate HIV antigen recognition by CTL have been identified. These data are discussed with regard to the eventual development of a vaccine and of functional immunotherapies.