The current risk of disease transmission through homologous blood transfusion has lead to a revival in the use of autologous blood. The development of a coagulopathy increases the usage of blood and blood products and therefore the risk of disease transmission. Blood salvaged at operation is subjected to physical and humoral activating factors. The potential systems to be activated are located either in the plasma or non red cell cellular elements. Homologous blood and blood salvaged at operation before and after washing was examined for activation of the plasma and cellular systems by measuring the presence of fibrin degradation products (xDP's), activated complement (C3a) and plasminogen activator and inhibitor activity from the plasma systems; and elastase, serotonin, lysophospholipids, leukotriene B4, lysoplatelet factor and phospholipase A2 from the cellular systems. The plasma systems were activated in the salvaged blood which had elevated levels of xDP's and C3a compared to the patient's blood (p less than 0.05). The products of cellular activation were also elevated in operatively salvaged blood (p less than 0.01 for all the above products). The levels xDP's were normal but the levels of C3a increased in stored blood. The levels of the cellular systems, elastase, serotonin and lysoplatelet activating factor, increased with the duration of storage of bank blood. Unwashed and aged stored blood contains potentially harmful products. Consideration should be given to removal of non red cell elements in blood stored for surgery.