ABSTRACT.Our purpose was to resolve the disagreement as to the number of calories expended per unit distance for walking and running. The caloric costs of walking and running one mile on a treadmill were calculated for eight men and eight women. The subjects walked at a speed of 82 ± 3 m/min (X ± SD) and each ran at a speed that was regarded subjectively as comfortable. The average speed at which the mile was run was 195 ± 25 m/min for men and 137 ± 4 m/min for women. The average R measured during the walk was 0.86 and during the run, 0.96. The gross caloric cost of walking was 1.08 ± 0.06 kcal/kg per mile for men and 1.15 ± 0.08 kcal/kg per mile for women, and the cost of running was 1.57 ± 0.09 kcal/kg per mile for men and 1.73 ± 0.09 kcal/kg per mile for women. The running required significantly more kcal/kg per mile than walking (P < 0.001) and the women used significantly more calories for both running and walking compared to the men (P < 0.01). The net caloric cost of walking was 0.76 ± 0.07 kcal/kg per mile for men and 0.83 ± 0.08 kcal/kg per mile for women, and the cost of running was 1.43 ± 0.08 kcal/kg per mile for men and 1.53 ± 0.09 kcal/kg per mile for women. The difference between the run and walk was highly significant (P < 0.001) and the women used significantly more calories than men for both activities (P < 0.05). Possible reasons for the small but statistically significant difference between men and women are discussed. It was concluded that running a given distance required more calories than walking the same distance.