This study was aimed to evaluate the possible changes caused by a single bout of moderate-intensity exercise in a hot environmental temperature on the immune function and on inflammatory markers. A total of 22 young male adults (VO2(max), 55.4 +/- 3.6 ml x kg(-1) x min(-1)) volunteered to participate in an exercise session of 60 minutes on a treadmill ergometer at moderate speed (60% of the maximum aerobic speed) in hot environmental conditions (35 degrees C and humidity 60%). Total leukocyte numbers, lymphocyte subsets (CD8+, CD4+, CD3+, NK and CD19+), cytokine production capacity by peripheral blood mononuclear cells (PBMCs) (IL-2, IL-4, IL-5, IL-10, IFN-gamma and TNF-alpha) as well as the concentration of several inflammation related proteins (ceruloplasmin, C-reactive protein (CRP), complement factors C3 and C4) were evaluated before and after exercise. The results show that leukocyte and neutrophil absolute values increased (P < 0.001) after the exercise period. In contrast, eosinophil values decreased (P < 0.05) after the exercise. In addition, ceruloplasmin, C3 and C4 values (P < 0.05) increased after exercise. No changes in T lymphocyte subsets, cytokine production, or CRP were observed. These data confirm previous studies suggesting that a 60 min exercise in a hot environment is enough to cause a physiologic adaptation to these special conditions leading to an increase of non-specific immune cells and promoting inflammatory processes. On the other hand, PCR values, lymphocyte subsets and the capacity of cytokine production by PBMC were not changed in a relatively short bout of exercise under these conditions in contrast with previous studies.