This study examined the validity of the CardioCoachCO2 metabolic system to measure oxygen capacity by comparison to a previously validated device. Fourteen subjects (8 men and 6 women; 25.9 +/- 6.6 years of age) completed 2 maximal graded exercise tests on a cycle ergometer. Subjects were randomly tested on the CardioCoachCO2 and Medical Graphics CardiO2/CP (MedGraphics) system on 2 separate visits. The exercise test included 3 submaximal 3-minute stages (50, 75, and 100 W for women; 50, 100, and 150 W for men) followed by incremental, 25 W, 1-minute stages until volitional fatigue (Vo2max). There was no significant difference between the CardioCoachCO2 and MedGraphics except at the 100 W stage (22.4 +/- 4.8 and 20.3 +/- 3.7 ml x kg(-1) x min(-1), p = 0.048, respectively). Spearman correlations demonstrated a strong correlation between the 2 devices at maximal Vo2 (R = 0.94). Bland-Altman plots demonstrated small limits of agreement, indicating that the 2 devices are similar in measuring oxygen consumption. This study indicates that the CardioCoachCO2 is a valid device for testing Vo2 at submaximal and maximal levels. Validation of this device supports the CardioCoachCO2 as a feasible and convenient method for testing participants and may be useful in the field or clinic.