Vaccination of mice with heat shock proteins (HSPs) derived from a tumor makes the mice resistant to the tumor from which the HSP was obtained. This phenomenon has been demonstrated with three HSPs—gp96, hsp90, and hsp70. Vaccination with HSPs also elicits antigen-specific cytotoxic T lymphocytes (CTLs). The specific immunogenicity of HSPs derives apparently, not from the HSPs per se, but from the peptides bound to them. These observations provide the basis for a new generation of vaccines against cancer. The HSP-based cancer vaccines circumvent two of the most intractable hurdles to cancer immunotherapy. One of them is the possibility that human cancers, like cancers of experimental animals, are antigenically distinct. The prospect of identification of immunogenic antigens of individual cancers from patients is daunting to the extent of being impractical. The observation that HSPs chaperone antigenic peptides of the cells from which they are derived circumvents this extraordinary hurdle. Second, most current approaches to cancer immunotherapy focus on determining the CTL-recognized epitopes of cancer cell lines. This approach requires the availability of cell lines and CTLs against cancers. These reagents are unavailable for an overwhelming proportion of human cancers. In contrast, the HSP-based vaccines do not depend on the availability of cell lines or CTLs nor do they require definition of the antigenic epitopes of cancer cells. These advantages, among others, make HSPs attractive and novel immunogens against cancer.