Adaptation to heat may occur through acclimatization or thermotolerance; however, the linkage of these phenomena is poorly understood. The importance of heat shock proteins (HSPs) in thermotolerance and differences in their accumulation in organisms adapted to the heat suggest a role for HSPs in acclimatization as well. The role of HSPs in heat adaptation of the whole organism and the interrelationships among heat adaptation, endotoxin tolerance, and cytokine resistance through HSPs are reviewed.