The aim of this study was to investigate the effect of ingesting sodium bicarbonate (SB) and sodium citrate (SC) on 400 m high-intensity swimming performance and blood responses. Blood pH, HCO3-, BE were significantly elevated from before loading to the pre-test (60 min post-ingestion) after SB ingestion, but not after SC ingestion. Performance times were improved by 0.6 % after supplementation of SB over placebo in 5 out of 6 participants (responders). In contrast, ingestion of SC decreased performance by 0.2% (p > 0.05). Monitoring the magnitude of the time-to-peak level rise in alkalosis may be recommended in order to individualize the loading time accordingly before the commencement of exercise.