Six pigs were used to study whether the collection of shed blood by means of surgical compresses instead of suction traumatizes such blood. In an in vivo part of the study, the whole blood volume of the pigs was retransfused after treatment with citrated compresses, and in an in vitro part the blood was treated extensively with compresses and analyzed. All animals survived, with a minor fall in hemoglobin after 48 hours and a rise in serum citrate concentration at the end of the experiment. A study of the coagulation system revealed no important change after retransfusion of compress-treated blood. In the in vitro part of the study, repeatedly squeezing blood from the compresses increased the concentration of free hemoglobin to a maximum of 5 g/l after ten squeezes, whereas platelets were numerically unchanged. The study indicates that collecting shed blood by means of surgical compresses may be a safe and efficient method.