Red blood cells are purified by separating whole blood, such as by centrifugation, to form a red blood cell fraction and a liquid fraction. The whole blood can be defibrinated or treated to prevent coagulation prior to separation. Preferably, the whole blood is bovine blood. The red blood cell fraction is then diafiltered to purify the red blood cells. The purified red blood cells can then be lysed to form a lysate of purified red blood cells. The purified red blood cells and the lysate of purified red blood cells are suitable for use in producing hemoglobin blood substitute.