Six healthy male subjects performed three exercise tests in which the power output was increased by 100 kpm/min each minute until exhaustion. The studies were carried out after oral administration of CaCO3 (control), NH4Cl (metabolic acidosis), and NaHCO3 (metabolic alkalosis). Ventilation (VE), O2 intake (VO2), and CO2 output (VCO2) were monitored continuously. Arterialized-venous blood samples were drawn at specific times and analyzed for pH, PCO2, and lactate concentration. Resting pH (mean +/- SE) was lowest in acidosis (7.29 +/- 0.01) and highest in alkalosis (7.46 +/- 0.02). A lower peak power output (kpm/min) was achieved in acidosis (1,717 +/- 95) compared with control (1,867 +/- 120) alkalosis (1,867 +/- 125). Submaximal VO2 and VCO2 were similar, but peak VO2 and VCO2 were lower in acidosis. Plasma lactate concentration was lower at rest and during exercise in acidosis. Although lactate accumulation was reduced in acidosis, increases in hydrogen ion concentration were similar in the three conditions. We conclude that acid-base changes influence the maximum power output that may be sustained in incremental dynamic exercise and modify plasma lactate appearance, but have little effect on hydrogen ion appearance in plasma.