To assess the psychological effects of exercise training in hemodialysis patients 4 dialysis patients, matched by age, sex, and medical history with 4 controls, received psychological testing before and after a 6-month period of exercise training. The trained patients had a 28% improvement in graded exercise treadmill stress test duration and a 13% improvement in aerobic capacity. This was associated with a significant reduction in anxiety and depression (p less than 0.06), but no measurable change in these moods occurred in the control groups. These results suggest that exercise training may improve psychological functioning in dialysis patients.