Eighteen hemodialysis, 12 chronic ambulatory peritoneal dialysis (CAPD), and 20 renal transplant patients performed maximal treadmill exercise tests. Heart rates and blood pressures were determined every minute and maximal oxygen consumption was measured directly. Exercise capacity as measured by VO2 max is low in dialysis patients and similar to sedentary normal individuals in renal transplant patients. Maximal heart rates were significantly lower in hemodialysis patients than transplant recipients. The lower exercise tolerance in end-stage renal disease indicates that most patients regardless of the treatment mode could benefit from attempts through exercise training to increase physical working capacity.