During high-intensity exercise, both pulmonary O2 uptake (VO2) and blood [lactate] continue to rise with time, suggesting that the so-called VO2 'slow component' (VO2SC) might be mechanistically linked to the development of a metabolic acidosis. We therefore hypothesised that a pre-exercise metabolic alkalosis achieved through the ingestion of sodium bicarbonate (SBC) might reduce the VO2SC. Seven healthy men completed step cycle exercise tests to a work rate requiring ~ 85% VO2 peak with and without prior ingestion of 0.3 g.kg-1 body mass of SBC. SBC ingestion resulted in a significant increase in blood pH immediately before (paired t-test; CON: 7.41±0.01 vs. SBC: 7.47±0.01; P<0.05) and throughout exercise. Neither the Phase II time constant (CON: 29±6 vs. SBC: 33±8 s) nor the amplitude of the fundamental VO2 response (CON: 2.31±0.36 vs. SBC: 2.33±0.25 L.min-1) were different between the conditions. However, SBC ingestion increased the time delay before the appearance of the VO2SC (CON: 120±19 vs. SBC: 147±34 s; P<0.05) and reduced the amplitude of the VO2SC (CON: 0.61±0.15 vs. SBC: 0.46±0.11 L.min-1; P<0.05). These results indicate that pre-exercise metabolic alkalosis induced by SBC ingestion has no effect on the Phase II VO2 kinetics but results in a 25% reduction of the VO2SC during high-intensity exercise.