1. The oxygen intake of four Olympic walkers was measured while walking and running at varying velocities on a treadmill at an altitude of 1800 m.2. The relation between O(2) intake and running at speeds between 8 km/hr and 21 km/hr was linear. The relation for walking at speeds up to 8 km/hr followed an upward concave curve. These findings were similar to results obtained at sea level by other investigators.3. For walking at speeds between 8 km/hr and 14.5 km/hr the relation of O(2) intake and velocity was a straight line having a slope twice that of running.4. Maximum O(2) intake in walking averaged 60.0 ml./kg/min (range 55.8-64.1 ml./kg/min) compared with 57.4 ml./kg/min (range 55.2-60.2 ml./kg/min) in running. An international class long distance runner serving as a control reached a maximum O(2) intake of 70 ml./kg/min.