The current increased participation in long distance running and endurance events brings new challenges to the physician. Adaptive changes of exercise must be differentiated from disease states. Left ventricular hypertrophy, Wenckebach rhythm, elevated creatine kinase (myocardial fraction), gastrointestinal bleeding, hematuria, hemoglobinuria, amenorrhea, and apparent anemia may all be exercise related. New syndromes have arisen--from "runner's high" to athletic amenorrhea. These dedicated athletes can be difficult patients. They are highly motivated and will continue training despite significant pain and danger of permanent damage. Speaking their language--carbohydrate loading, "the bonk," "slow twitch," "the wall"--is helpful in their treatment. Traditional health problems are less likely to bring the fitness addict to the physician than some new and peculiar disorders.