In humans, washing stored blood products prior to transfusion reduces storage lesions and the potential for transfusion reaction, but the effectiveness of washing units of canine whole blood is unknown. The objective of this study was to determine if a manual method of washing of stored whole blood units reduced storage lesions without adversely affecting erythrocytes. Units of canine whole blood were stored for 28 days and manually washed three times with sterile .9% NaCl. Following the first wash, there was a decrease in serum potassium (P<.0001), lactate (P<.0001), pH (P=.0110), pCO2 (P<.0001), TCO2 (P<.0001), arachidonic acid (P<.0001), and thromboxane B2 (P=.0417), and increases in iCa (P=.0494), iMg (P=.0024), MCV (P<.0001), MCHC (P=.0093), RDW (P=.0009), hemoglobin (P=.0011), and MCF (P=.0006). No bacterial growth was identified on the post-transfusion samples. Manual washing of stored blood significantly reduces storage lesions after a single wash and additional washing may cause in vitro hemolysis.