The changes in pH, pCO2, pO2, based excess, standard bicarbonate and lactic acid during storage of canine blood 24 hours at different temperatures were measured (table I a, b) and illustrated (figs. 1 and 2). A correction table (table V) for determination of the initial acid-base data is constructed based upon regression equations (table IV) of the in vitro changes during storage of the blood. The changes in the acid-base values of canine blood differ from that of bovine and human blood (tables II and III).