A rational approach to the use of blood entails careful assessment of blood loss in the individual patient and a clear awareness of the advantages and disadvantages which may follow the use of whole blood. The use of red cell concentrates in preference to whole blood has therapeutic and immunological advantages for a majority of patients. Predictable changes which follow massive transfusion must be assessed and appropriate steps taken to minimize any undesirable results in the patient. A protocol for emergency transfusion is outlined.