Introduction and objective. Heat stress induces the expression of genes encoding heat-shock proteins and immune response mediators. The aim of this study was to determine the differences in the expression of genes encoding heat-shock proteins 70 kDa and27 kDa, interleukin 6, interleukin 10and C-reactive protein, between athletes and non-athletes after sauna bathing. Materials and method. Athletes (n=9) and non-athletes (n=9) were exposed to a Finnish sauna twice during one session at a temperature of 98.2 °C and humidity of 10% ± 2%, with a 5 min break for cooling down under a shower. The groups did not differ in terms of age, height or body mass. Blood samples were taken before and after sauna exposure in order to assess gene expression, using reverse transcription polymerase chain reaction. Results. Differences were observed in leukocyte mRNA levels of tested genes between athletes and non-athletes. In the non-athlete group, all the tested genes were expressed at higher levels as a response to the same heat challenge. Conclusion. It appears that expression of stress-related genes induced by heat stress is dependent on the level of physical activity.