During the next few years, several top-level sport competitions involving endurance running, such as the marathon, will occur in hot/humid Asian summertime weather. These competitions include the World Athletics Championships, the World Student Games and the Summer Olympic Games. Well prepared athletes have a fitness level so high that they can produce more metabolic heat than can be dissipated, and thus run the risk of encountering heat illness unless they fine-tune their pace, making it compatible with manageable heat production. The ideal starting time for such long races would be early evening, so that athletes encounter steadily improving weather (less sun, gradual cooling and minimum rise in humidity). However, current plans for competition scheduling have the marathon races starting in the early morning hours. Thus, as the race develops and athletes experience a trend towards dehydration and energy depletion, weather conditions will likely deteriorate and impact negatively upon performance. Suggestions are provided for optimising performance under these circumstances.