The working capacities of children tested on a bicycle ergometer in the spring and again in the fall showed no significant differences. The pulse rate method of determining working capacity in children has been validated by additional oxygen consumption studies. Oxygen consumption is proportional to the work load even with pulse rates from 170 to 215 beats per minute. The physical working capacity as determined by the pulse rate method shows a direct relationship to maximal oxygen consumption or oxygen pulse ratio. The determination of oxygen consumption would appear to offer no particular advantages, and physical working capacity of children may be determined with confidence by simply determining the pulse rate at known work loads. The working capacity of those in poor condition may be slightly underestimated when pulse rate methods are used.