SIV and HIV-2 infection of macaques has become a widely used model to study human HIV infection because the pathogenicity of, as well as the immune responses to, the viruses can be examined conveniently. In particular, the cellular immune responses to SIV or HIV-2 have been investigated thoroughly. This review summarizes the knowledge about helper and cytotoxic T-cell immunity in macaques, and it discusses the relevance and applications of this primate animal model for AIDS research.