A case of severe anemia complicated with lactic acidosis (blood lactic acid concentration 17.5 mmol/l) is presented. Circulatory failure and other causes of lactic acid accumulation could be excluded. Transfusion treatment resulted in a rapid correction of the metabolic derangements. Activation of anaerobic metabolism is prevented in anemia by the highly efficient compensating mechanisms of the organism. Only an extreme fall of the blood hemoglobin concentration below 2 g/dl may result in lactic acidosis.