Platelet function tests (bleeding time, platelet adhesiveness, platelet factor 3 release, and platelet aggregation to ADP) were done on a group of severe factor VIII deficient hemophiliacs before, during, or after transfusion therapy with cryoprecipitate or factor VIII concentrate. Mild decreased platelet function was seen in nonbleeding hemophiliacs after a single transfusion of cryoprecipitate. More severe abnormalities of platelet function were observed in a group of patients receiving factor VIII therapy for severe hemorrhages or in the postoperative period. Several of these intensively transfused patients bled when their circulating factor VIII level was normal or near normal. In one patient, who was studied repeatedly, prolongation of the thrombin time and partial thromboplastin time occurred in association with high levels of fibrinogen. Fibrin split products (fsp) were increased in most of the patients during bleeding episodes. Mixtures of cryoprecipitate or factor VIII‐concentrate with normal plasma contained increased protamine precipitable material and fibrin split products. Paradoxical bleeding can occur in intensively transfused hemophilic patients and may be related to either abnormal platelet function or increased levels of circulating fibrin monomer, fsp, or fibrinogen interfering with thrombin‐fibrinogen interact