This study investigated the renal and endocrine responses to arm exercise in persons with spinal cord injury (SCI) under euhydration conditions (ad libitum drinking of water) and determined the physiological effects of exercise on renal function in these subjects. Eleven SCI (spinal lesions between T6 and L1, American Spinal Injury Association impairment scale A) and 14 able-bodied (AB) persons first rested for 1 h in a sitting position, before undergoing 2-h arm-crank ergometer exercise at 60% of maximum oxygen consumption followed by a 2-h recovery period. On another day, all subjects participated in a time control study (5 h of rest condition in sitting position). Urine and blood samples were collected hourly. There were no differences in mean blood pressure between the two groups. SCI patients showed attenuated increase in plasma adrenaline and increase in plasma aldosterone compared with AB controls, but similar changes in human atrial natriuretic polypeptide, plasma renin activity and plasma antidiuretic hormone following the exercise. Creatinine clearance, osmolal clearance, free water clearance and fractional excretion of Na(+) did not change during exercise in any of the subjects. These findings suggested that activated aldosterone and attenuated adrenaline responses during exercise in SCI could be due to adaptation to disordered sympathetic nervous system triggered to maintain renal function. The results showed no exercise-related adverse effects on renal function in hydrated subjects with SCI.