Acid-base changes have been followed in 8 babies during exchange transfusion with ACD blood. During exchande transfusion mild metabolic (pH 7.323, pCO_2 38.3 mmHg, BE-6.0 mEq/?) developed finally but did not be needed to correct with buffer if using the warm stored blood. Certain practical impliations of these finding and 2, 3-DPG are discussed.