While expression of HSPs may be induced by heat tive immunity to cancer challenges, ie, by the very shock, glucose deprivation, and other stresses, most HSPs are present in abundant levels even under normal conditions (reviewed by Lindquist and Craig, 1988). Recent years have seen the emergence of compelling evidence that HSPs possess unique properties that permit their use in generating specific immune responses against cancers and infectious agents; these applications suggest a critical role for HSPs in adaptive and innate immunity in vivo and raise the possibility that the HSPs are the primordial molecules involved in host defense.