The U.S. Army's fluid replacement guidelines emphasize fluid replacement during hot weather training to prevent degradation of performance and minimize the risk of heat injury. Little consideration has been given, however, to possible overhydration and development of water intoxication. Sufficient epidemiological evidence is available to demonstrate an increasing incidence of water intoxication during military training. This article summarizes the development and validation of revised fluid replacement guidelines for hot weather training. The end product is an easy-to-read table that provides the user with the appropriate hourly work time and fluid intake to support work during hot weather training. The guidelines include the range of hot weather conditions likely to be encountered during military training and cover a broad range of military activities. It is expected that the revised guidelines will sustain hydration and minimize the number of heat injuries during military training while protecting the soldier from becoming sick from overdrinking.