Six males performed cycle ergometer exercise on two occasions in random order. Each exercise was preceded by a 2-h period in which matched capsules were administered orally, containing either starch (C) or NaHCO₃ (E) in a dose of a 0.2g•kg^-1 body wt; pre-exercise blood pH and [HCO₃^-] were 7.34±0.01 and 23.7±0.5mM (mean±S.E.) for the C study, and 7.41±0.01 and 28.6±1.3mM for the E study (p<0.001 and p<0.01, respectively). Exercise was continuous and maintained for 10min at 40% of maximal oxygen uptake (40% V_O2max), followed by 15min at 12W above the respiratory compensation threshold ([+RCT]) which was determined by the increase of the ventilatory equivalent for carbon dioxide (VE•V_CO2^-1), and for as long as possible at 95% V_O2max. Endurance time at 95% V_O2max was significantly longer in E than in C (2.98±0.64min vs. 2.00±0.44min, p<0.05). The rate of increase in arterialized venous lactate (LA) was higher in E than in C from rest to exercise at [+RCT], while there was no significant difference in the hydrogen ions ([H⁺]). Consequently, [H⁺]•LA^-1 (nM•mM^-1) was significantly lower in E than in C. The change of VE•V_CO2^-1 was shifted downward in E compared to C during exercise with the lowest value being observed at the same exercise stage. These results suggest that the respiratory responses to exercise are not affected by the higher level of [HCO₃^-] induced by NaHCO₃ ingestion, and appear to reflect the net change of plasma [HCO₃^-] or [H⁺]. Also, induced metabolic acidosis has little effect on [H⁺] appearance in blood.