Patients with severe lactic acidosis and oliguria who receive large amounts of sodium bicarbonate may develop fluid overload and hyperosmolarity. We infused massive amounts of isotonic sodium bicarbonate and simultaneously removed the excess sodium and water with ultrafiltration if 2 patients with lactic acidosis. The first patient received 1,125 mmol of bicarbonate over 4.5 h with a rise in pH from 7.00 to 7.36 and in HCO<sub>3</sub> from 3.5 to 15.7 mmol/l. The second received 968 mmol of bicarbonate over 5.25 h with a rise in pH from 7.00 to 7.27 and in HCO<sub>3</sub> from 5.3 to 14 mmol/l. Blood pressure remained stable or rose, electrolytes normalized, excess fluid was removed, and a higher pH was maintained. Isotonic bicarbonate infusion with simultaneous ultrafiltration is a safe and rapid method of correcting the metabolic status of patients with severe lactic acidosis who have not responded to standard therapy.