Seventy children, ranging in age from 7 to 14 years, performed a maximal exercise test on a treadmill with determination of the anaerobic threshold (AT) by two methods: (1) with the gas exchange method the ventilatory anaerobic threshold (VAT) was identified by the increase in the ventilatory equivalent for O2 uptake without a concomitant increase in the ventilatory equivalent for CO2 output and (2) with the method proposed by Conconi, the AT was taken at the point beyond which the increase in work intensity exceeded the increase in heart rate and the linearity of the work rate/heart rate relationship was lost. The AT values measured with the two methods were correlated (r = 0.80, P less than 0.001). This result confirms, also in children, the validity of the simple Conconi method: It can be used particularly for the determination of the individual optimal intensity of training.