The review concerns properties and function of heat shock proteins (hsp) in the eukaryotic cell. The factors inducing Hsps' expression are considered with the emphasis on the fact that most of these agents are able to affect the function of peptide-synthesizing and protein-modifying machineries. The common outcome of this effect is accumulation of wrongly assembled protein structures which results in activation of heat shock transcription factors. The major property of proteins belonging to Hsp70 and Hsp90 is their chaperonic activity or the ability to bind newly synthesized or damaged polypeptides followed by restoration of the native structure of the latter. In this activity Hsp70 and Hsp90 are assisted by other proteins, and the work of such chaperonic systems is described. The function of the major stress protein Hsp70 in the eukaryotic cell was analysed, and on the base of a huge amount of data in has been resumed that proteins of this family constitute one of the most abundant systems of cell protection against cytotoxic factors. In the concluding part of the review we present some ways of application of our knowledge of Hsp in ecology, for analysing biological pollution, and in medicine, for increasing tissue or organismal resistance to injuring factors.