Abstract Among 22 patients studied during cardiac arrest, 10 had predominantly respiratory, and eight metabolic acidosis. Most patients with metabolic acidosis had myocardial infarction, had an arterial pH of 7.15 to 7.35, and appeared to be benefited by sodium bicarbonate with or without hyperventilation. In those with respiratory acidosis, chiefly patients with pulmonary problems, the pH was 6.86 to 7.09 in eight, hypercapnia was prevalent, alkali therapy seemed less effective, and improved ventilation appeared to be the major therapeutic objective.