Ethylene glycol intoxication produces a severe metabolic acidosis with an increased anion gap. We examined three patients with this intoxication to identify the organic acids that cause acidemia in humans and to determine how effectively these acids can be removed during dialysis. All patients had markedly elevated glycolic acid levels of more than 7 meq/L and two patients had lactic acidosis, with lactic acid levels of greater than 5.0 meq/L. Hemodialysis clearance of glycolic acid was 105 mL/min, and 159 meq was removed in 3 hours. After hemodialysis using a bicarbonate dialysate, the mean anion gap decreased from 34 to 23 meq/L; the mean serum bicarbonate concentration increased from 5.5 to 20 meq/L. Therefore, glycolic and lactic acids are important in the acidosis caused by ethylene glycol intoxication in humans. Hemodialysis treatment with a bicarbonate dialysate is an efficient method for removing glycolic acid and resolving acidemia.