A defect in T-lymphocyte suppressor cell function has been reported to occur in a number of autoimmune diseases. The influence of exercise on suppressor cell function has not been determined in individuals with autoimmune diseases, nor has it been determined in healthy individuals. The purpose of this investigation was to determine the effect of an acute bout of submaximal exercise on suppressor cell function in healthy males. Each subject (n=10) completed an exercise trial (E; 1 h of cycle ergometry at 70.6% of maximal oxygen uptake, followed by 2 h of recovery) and a resting trial (R; 3 h of seated rest), separated by at least 1 week. Treatment (E or R) order was counterbalanced. Venous blood samples were obtained pre-exercise (PRE), immediately after exercise (POST), and 2 h post-exercise (2HPOST), and at the same time points in the R trial. Lymphocyte phenotype percentages were determined by flow cytometry, while concanavalin- A-induced suppressor cell function was determined on peripheral blood mononuclear cells. No change was observed in the percentage of T-cytotoxic/suppressor cells. Suppressor cell function was significantly different between treatments, with the POST E value [mean (SD) 56.8 (1.6)%] being higher than the POST R value [41.7 (1.9)%]. No significant difference was observed 2HPOST. In conclusion, acute submaximal exercise resulted in a transient increase in suppressor cell function in healthy males.