For nearly 40 years, scientists and elite endurance athletes have been investigating the use of altitude in an effort to enhance exercise performance. While the results of many early studies on the use of altitude training for sea level performance enhancement have produced equivocal results, newer studies using the 'live high, train low' altitude training model have demonstrated significant improvements in red cell mass, maximal oxygen uptake, oxygen uptake at ventilatory threshold, and 3000m and 5000m race time. For the marathoner looking to add altitude training to their peak performance plans, residence at an altitude of 2000-2500m, a minimum of 20 hours per day, for 4 weeks, appears to hold the greatest potential for performance enhancement. Based on published mathematical models of marathon performance, a marathoner with a typical or average running economy who performed 'live high, train low' altitude training could experience an improvement of nearly 8.5 minutes (or approximately 5%) over the 26.2-mile race distance.