Background. Shed nonwashed blood and shed washed red blood cells (RBC) are being used as alternatives to allogeneic liquid-preserved RBC for patients during thoracic and cardiovascular surgical procedures. Methods. Mongrel dogs were bled a volume of blood into the abdominal cavity and the shed blood was reinfused as nonwashed blood or washed RBC. The Cr-51 RBC volumes were measured before, immediately after, and 24 hours after the exchange transfusion to assess the recovery of the shed RBC and the 24-hour postftansfusion survival. Compatible dogs were given allogeneic transfusions of Cr-51-labeled nonwashed blood and washed RBC, and 24-hour posttransfusion survival and half-life were measured. Results. Immediately after the 100% exchange transfusion, the recovery value was 62% for the nonwashed shed blood and 82% for the washed RBC. Both the nonwashed blood and the washed RBC had 24-hour posttransfusion survival values of 90% and normal oxygen transport function after the exchange transfusion. Compatible allogeneic Cr-51-labeled nonwashed blood and washed RBC had normal 24-hour posttranfusion survival and Cr-51 half-life values. Conclusions. The survival, function, and hemolysis of shed nonwashed blood and shed washed RBC were similar to fresh blood in the dog that underwent a 100% exchange transfusion. (C) 2001 by The Society of Thoracic Surgeons.