We measured the gas exchange response to exercise in 109 normal children (51 girls and 58 boys, ranging in age from 6 to 17 yr old) using noninvasive breath-by-breath techniques. The protocol consisted of cycle ergometry in which the work rate increased in a linear manner (ramp forcing function) until the limit of the subject's tolerance was reached. We measured the maximal oxygen uptake () and the at the anaerobic threshold (AT). We found that both of these parameters were highly correlated with increasing height, and that for both the AT and , the values for boys were significantly higher than girls. We compared our results of to those obtained by Åstrand over 30 years ago using different techniques. When boys and girls were considered together, there were no significant differences between our study and Åstrand's; however, girls in our study had significantly lower values for than did girls in Åstrand's study. These data provide normal values for both and AT and can be used to evaluate the exercise impairment resulting from disease in children.