Extracellular heat shock protein with molecular weight of 70 kDa is a signal molecule of the immune system. It is secreted by the peripheral blood, liver and muscle cells in response to physiological, thermal, and mental stresses. The main goal of our study was to compare the levels of expression of heat shock protein (70 kDa) matrix ribonucleic acid in leukocytes and serum concentrations of the protein before and after physiological stress. In order to solve this problem, we developed enzyme immunoassay of serum heat shock (70 kDa) protein concentration and a method for evaluating the expression of matrix ribonucleic acid of this protein in leukocytes by the real time PCR. The concentration of 70 kDa heat shock protein in the serum increased 1.7 times as a result of even a short-term highly intense physiological stress, while the expression of its matrix ribonucleic acid in leukocytes increased 1.5 times. The individual features determine the response to physiological stress. Probable sources of 70 kDa heat shock protein are discussed.