Purpose Enteric-coated sodium bicarbonate (NaHCO 3) can attenuate gastrointestinal (GI) symptoms following acute bicarbonate loading, although the subsequent effects on exercise performance have not been investigated. The purpose of this study was to examine the effects of enteric-coated NaHCO 3 supplementation on high-intensity exercise performance and GI symptoms. Methods Eleven trained male cyclists completed three 4 km time trials after consuming; a placebo or 0.3 g•kg-1 body mass NaHCO 3 in enteric-coated or gelatin capsules. Exercise trials were timed with individual peak blood bicarbonate ion concentration ([HCO 3-]). Blood acid-base balance was measured pre-ingestion, pre-exercise, and post-exercise, whereas GI symptoms were recorded pre-ingestion and immediately pre-exercise. Results Pre-exercise blood [HCO3 − ] and potential hydrogen (pH) were greater for both NaHCO 3 conditions (P < 0.0005) when compared to placebo. Performance time was faster with enteric-coated (− 8.5 ± 9.6 s, P = 0.044) and gelatin (− 9.6 ± 7.2 s, P = 0.004) NaHCO 3 compared to placebo, with no significant difference between conditions (mean difference = 1.1 ± 5.3 s, P = 1.000). Physiological responses were similar between conditions, although blood lactate ion concentration was higher with gelatin NaHCO 3 (2.4 ± 1.7 mmol•L-1 , P = 0.003) compared with placebo. Furthermore, fewer participants experienced GI symptoms with enteric-coated (n = 3) compared to gelatin (n = 7) NaHCO 3. Discussion Acute enteric-coated NaHCO 3 consumption mitigates GI symptoms at the onset of exercise and improves subsequent 4 km cycling TT performance. Athletes who experience GI side-effects after acute bicarbonate loading may, therefore, benefit from enteric-coated NaHCO 3 supplementation prior to exercise performance.