During prior acclimatization, mineworkers acquire tolerance against the adverse effects of working in a warm environment. In this article, the possible involvement of heat shock proteins as mediators of acclimatization is proposed. Acclimatization is compared with preconditioning. Preconditioning of isolated cells or organs by prior exposure to a temperature higher than normal or exposure to an ischaemic insult endow tolerance on them when later confronted with a severe ischaemic stress. This tolerance is possibly mediated by heat shock proteins induced by the heating or ischaemic preconditioning episode. Functioning of the induced heat shock proteins may therefore underlie the protective mechanisms in both acclimatization and preconditioning.