Excess free-radical formation has been hypothesized to contribute to cancer, atherosclerosis, aging, and exercise-associated muscle damage. Antioxidant supplements such as vitamin C, vitamin E, and beta-carotene have been touted as beneficial for enhancing exercise performance and for preventing certain diseases. Before physicians routinely recommend supplements to prevent exercise-associated damage, more study will be required. Recommendations for the prevention of cardiovascular disease and cancer are more complex. Because study results have been contradictory, individual supplement recommendations must be offered with caution. Physicians must be cognizant of which supplements patients are taking and be prepared to discuss risks and benefits. The most beneficial prescription is probably a daily diet containing five to seven servings of fruits and vegetables.