The purpose of this study was to investigate the differences in kinetics of CO₂ output (V_CO2) during incremental exercise in sprinters (S), middle (MD), and long distance runners (LD). In the steady state exercise, the V_CO2 was linearly related to the O₂ uptake (V_O2). In the incremental exercise below anaerobic threshold (AT), the V_CO2 was also linearly related to the V_O2. The difference between the V_CO2 estimates from the regression lines obtained in steady state and incremental exercise was added from the start of exercise up to a given time. The added values were defined as CO₂ stores. The CO₂ stores per body weight were significantly related to mixed venous CO₂ pressure (PV_CO2) determined by the CO₂ rebreathing method. The slopes of the regression lines between PV_CO2 and CO₂ stores per body weight were not different among three groups. If V_CO2 above AT is estimated from the VO₂ using the regression line obtained in incremental exercise below AT, the estimated V_CO2 is lower than the measured V_CO2. The sum of the differences in V_CO2 up to a given time was defined as CO₂ excess. The CO₂ excess per body weight was significantly related to ΔLA (the difference between blood lactates at 5min after exercise and at rest). The ratios of CO₂ excess per body weight to ΔLA were 3.30±1.49, 4.16±2.33, and 5.55±2.05 for sprinters, middle, and long distance runners, respectively. This ratio obtained in sprinters was significantly lower than that in long distance runners (p<0.01).