THE SCIENCE OF fluid replacement in athletic training, particularly with regard to American football players, has advanced during the past 3 decades. This advance has resulted in substantial decreases in heatstroke-related deaths during summer training sessions. Recent trends in football heatstroke fatalities toward significant increases may, in part, be attributable to or aggravated by the use of dietary supplements. Credible scientific evidence has been found that amphetamine derivatives and the ergonomic aid creatine may contribute to subclinical dehydration and heatstroke in selected individuals. Caution is urged in the education and evaluation of football players who train during the hot summer months.