Six healthy subjects performed four exercise studies in random order on separate days: a control study, metabolic acidosis induced by ammonium chloride, metabolic alkalosis induced by sodium bicarbonate, and respiratory acidosis induced by 5% CO2 inhalation. The subjects exerted maximal force on the pedals of a constant-velocity cycle ergometer at 100 rpm for 30 s; torque was measured and power calculated. Arterialized venous blood was sampled, and plasma lactate concentrations was measured immediately after and at 2-min intervals for 10 min following exercise. Although maximal peak power and total work, for the 30-s test, were lower in the two acidosis conditions, this effect was not statistically significant. Plasma lactate 30-s postexercise was lower in metabolic acidosis (2.8 +/- 1.6 mmol X 1(-1) (mean +/- SD) and respiratory acidosis (1.5 +/- 0.8 mmol X 1(-1) than in placebo conditions (5.9 +/- 3.3 mmol X 1(-1) and metabolic alkalosis 7.8 +/- 4.2 mmol X 1(-1). These differences were maintained but lessened during 10 min of recovery. In contrast to previous studies, which showed a marked reduction in endurance time during sustained heavy exercise, reductions in blood pH are associated with only small reductions in the total work performed in 30 s of maximal exercise. A delayed and smaller accumulation of lactate in plasma was observed following exercise during acidosis.