We administered dichloroacetate, which prevents or reverses hyperlactatemia in animals and lowers plasma lactate levels in human beings, to 13 patients with lactic acidosis of various causes. All had hypotension, and their acidemia had resisted treatment with sodium bicarbonate. The metabolic effects of dichloroacetate were evaluated in 11 patients. In seven dichloroacetate significantly reduced the level of arterial blood lactate (P<0.005) from the base-line value and raised the levels of arterial blood bicarbonate (P<0.02) and arterial pH (P<0.005). In six of these seven, the acidemia resolved completely with therapy. In 10 of the 13 patients systolic blood pressure increased by 10 to 40 mm Hg, and 4 patients had a 21 per cent increase in cardiac output (P<0.02). Despite improvement in their lactic acidemia, all patients but one died of their underlying disease. No serious drug-related toxicity occurred. We conclude that dichloroacetate is a safe and effective adjunct in the treatment of patients with lactic acidosis, although the ultimate prognosis may depend on the underlying disease. (N Engl J Med 1983; 309:390–6.)