Fourteen maintenance hemodialysis patients volunteered to participate in a 6-month program of exercise training. The exercise was performed on a stationary bicycle during the hemodialysis treatment. Six maintenance hemodialysis patients served as control without exercise training. Exercising patients participated in 91% of all possible exercise sessions. The exercise group showed a significant (23%) increase in maximal oxygen consumption over the 6 months. No change in exercise capacity resulted in the control group. Five of eight hypertensive patients in the exercise group decreased or discontinued antihypertensive medications. No changes occurred in hematocrit or lipid profiles in either group. We conclude that exercise training during the hemodialysis treatment is technically feasible and safe for appropriately screened patients and will increase exercise capacity, and in some patients improve blood pressure control. Exercise during dialysis also improves compliance to regular exercise and facilitates supervised exercise sessions, which are desirable in this patient group.