Clinical and experimental studies on the influence of massive preserved blood transfusions on clotting mechanism of recipient were done. The most striking change observed in the studies was profound thrombocytopenia, which was considered a significant factor of hemorrhagic tendency following massive preserved blood transfusions. Disturbance of coagulation factors were mild relatively. Fibrinolysis and increasing of heprain-like substance were also found. Especially, the former was significant in the case of Pulmonary sugery. Influence of vascular factor was also expected.