AbstractOur earlier observations (Clin. Res. Proc. 2, 61, 1954) on severe bleeding after administration of numerous (10 or more) transfusions to replace blood loss during surgery have been extended to 31 cases. Not only was hemorrhage striking during surgery, but showers of petechiae also were observed in some patients afterwards. Most cases were either patients undergoing cranial surgery, or patients with liver disease. Analysis of their hemostatic mechanism indicated, in most cases, severe thrombocytopenia with corresponding findings (poor clot retraction, poor utilization of prothrombin, prolonged bleeding time and positive tourniquet test); thrombocytopenia was transitory in some cases, persistent in others (3–5 days); in six cases, increased fibrinolytic activity of serum; in seven cases, reduced anti-hemophilic globulin and, in nine cases, reduced labile factor activity of plasma. Blood, calcium and citrate levels were normal.Etiology of bleeding and its most salient feature, thrombocytopenia, remained obscure. A number of mechanisms were investigated and the following explanations appeared likely: a) platelets, antihemophilic globulin, labile factor were steadily lost through bleeding, while administered “blank” blood was relatively poor in them. Thus, they were insufficiently replaced. Perhaps this becomes evident only when bone marrow, liver cannot promptly respond with accelerated production of platelets, clotting factors. Thus, patients with liver disease were particularly prone to show this type of hemorrhagic diathesis; b) normal plasma contains a fraction which depresses platelet count in vivo (Proc. Soc. exp. Biol., N.Y. 79, 623, 1952). Administration of large quantities of plasma might have emphasized this effect.Routine administration of compatible blood, freshly collected in plastic bags and isolated platelets reduced bleeding accidents. Either this technic supplied viable platelets or the activity of platelet-reducing fraction was less marked in fresh unadulterated than in stored plasma. In about one third of cases, administration of platelets helped to correct or reduce bleeding phenomena.