Heat shock proteins (Hsp) are the group of proteins observed in both prokaryotic and eukaryotic cell types. Hsp synthesis takes place in response to many environmental conditions, including ultraviolet radiation, heavy metal ions, hypoxia and toxic agents. Many authors have suggested that Hsp can be used in immunoprophylaxis, yet Hsp70 proteins expressed in bovine leukocytes have not been fully characterized. Hence the aim of this study was to evaluate the expression of Hsp70 proteins in bovine leukocytes exposed to temp. 41degrees C. The material for the study consisted of bovine white blood cells incubated at 41 degrees C for 2 hours. SDS-Page electrophoresis, Western blotting, and two-dimensional electrophoresis (2D) were performed to estimate the proteins obtained. The results of the study confirmed the influence of the temperature of 41 degrees C on induction of Hsp70 in bovine leukocytes. These proteins were mainly localized within molecular mass 70kDa. Some of the proteins with molecular mass from 20 to 50 kDa also showed positive reactions in Western blotting with anti-Hsp70 antibodies. Analysis of 2D electrophoresis showed a change in the localization of these proteins in the pH gradient. It can be postulated that analysis of Hsp70 expression in bovine leukocytes can be a very helpful marker for evaluating an organism's adaptation to environmental heat stress. The proteins obtained also showed immunological reactivity with rabbit antibodies in Western blotting reactions, indicating that they can be used as protective factors in the pathogenesis of many diseases.