These results demonstrate that some of the metabolic complications of chronic uremia treated with maintenance hemodialysis are related to the deterioration in physical fitness and strength that accompanies this chronic disease. Exercise training increased the physical work capacity, improved the lipid profile, normalized insulin sensitivity and glucose metabolism, and lowered the dose of antihypertensive medications required by some of the patients. These changes occurred in the absence of significant changes in diet or body weight. Furthermore, during an equivalent period of follow-up there was a significant deterioration in the lipid profiles of sedentary controls. Thus, exercise training has the potential to reduce the prevalence of many of the medical conditions thought to promote atherogenesis in hemodialysis patients. In addition, there was a significant improvement in the degree of anemia of the exercising patients. None of these metabolic and physiological changes could be attributed to factors related to changes in dialysis scheduling or technology, medications, or diets. Exercise training was associated with an improvement in the mood, level of depression, and psychosocial functioning of these patients; the sedentary controls either became more depressed or reduced their participation in pleasant, socially oriented activities. This raises the possibility that exercise training may have the potential to return some dialysis patients to a more normal social lifestyle, perhaps improving their socioeconomic status and reducing their dependency. These are extremely optimistic possibilities that could have far-reaching implications for the hemodialysis population. The dramatic improvements in lipid and glucose metabolism, hematologic function, blood pressure and work capacity in the exercising patients indicates that aerobic physical training is an effective therapeutic modality with a wide spectrum of effects on many pathologic processes previously thought to be a consequence of chronic uremia. Not only were there major biochemical changes as a result of exercise training, but the psychosocial functioning of these dialysis patients improved. Some of the physiologic changes, such as the increase in work capacity, greater strength and energy, and the rise in hematocrit, contributed to the psychological improvements, but in some patients accomplishing the goal itself (for most a 1-mile jog was the ultimate) seemed sufficient. There are a multitude of potential long-term benefits of exercise training programs for hemodialysis patients.(ABSTRACT TRUNCATED AT 400 WORDS)