The net oxygen cost of level and grade running was determined in three men-the author and two champion runners. The horizontal costs for the three were in agreement at the lower rates and for the two runners at high rates. A curve enables one to estimate the cost of horizontal walking and running and also of the horizontal component of grade walking and running. With this as a basis the cost of the vertical component in grade walking was found to be 1.53 ml/m·kg for the author and 1.31 ml/m·kg for one of the runners in both walking and running. This latter value and the curve relating the cost of the horizontal component to the rate of walking and running were used to estimate the cost of grade walking and running for seven other champion runners. The estimates checked closely with the observed cost in five. Marathoner DeMar was more efficient and the seventh runner was less efficient than predicted. champion athletes; work performance; work efficiency; oxygen cost of climbing Submitted on April 13, 1964