Oral ingestion of sodium bicarbonate (bicarbonate loading) has acute ergogenic effects on short-duration, high-intensity exercise. Because sodium bicarbonate is 27% sodium, ergogenic doses (i.e. 300 mg·kg−1) result in sodium intakes well above the Dietary Reference Intakes upper limit of 2300 mg/day. Therefore, it is conceivable that bicarbonate loading could have hypertensive effects. Therefore, we performed a double-blind cross-over trial to evaluate the hypothesis that bicarbonate loading increases resting and exercise blood pressure (BP). A secondary hypothesis was that bicarbonate loading causes gastrointestinal distress. Eleven endurance-trained men and women (exercise frequency, 4.6±0.4 sessions/wk; duration, 65±6 min/session) underwent testing on two occasions in random sequence: once after bicarbonate loading (300 mg·kg−1) and once after placebo ingestion. BP and heart rate (HR) were measured before bicarbonate or placebo consumption, 30 minutes after consumption, during 20 min of steady state submaximal cycling exercise, and during recovery. Bicarbonate loading did not affect systolic BP during rest, exercise, or recovery (p=0.38 for main treatment effect). However, it resulted in modestly higher diastolic BP (main treatment effect, +3.3±1.1 mmHg, p=0.01) and higher HR (main treatment effect, +10.1±2.4 bpm, p=0.002). Global ratings of gastrointestinal distress severity (0–10 scale) were greater after bicarbonate ingestion (5.1±0.5 vs. 0.5±0.2, p<0.0001). Furthermore, 10 of the 11 subjects (91%) experienced diarrhea, 64% experience bloating and thirst, and 45% experienced nausea after bicarbonate loading. In conclusion, although a single, ergogenic dose of sodium bicarbonate does not appear to have acute, clinically important effects on resting or exercise BP, it does cause substantial GI distress.