The effects of aspirin treatment on kidney excretory function were investigated in treadmill-exercised men. Six individuals ran for 30 min at 70% of their maximal oxygen consumption. Exercise tests were conducted for control and aspirin-treated conditions. Aspirin (3.25 g/d) was administered for 3 d prior to testing. Experiments were carried out with the subjects non-hydrated and hydrated (4 ml H2O/kg body weight). Aspirin treatment did not influence the alterations in creatinine clearance, urine volume, osmolar clearance, and/or sodium and potassium excretion seen with exercise. The only effect of aspirin was observed in the recovery samples of the non-hydrated tests in which aspirin treatment significantly decreased urine volume and increased urine specific gravity, osmolality, and the urine/plasma osmolality ratio. These results suggest that aspirin treatment does not have any significant effects on the renal excretory response to short-term moderate exercise.