Platelet adhesiveness and aggregation were studied in three patients with congenital afibrinogenemia. The results obtained may be summarized as follows: The retention of platelets to a glass-bead filter determined with the Salzman method was significantly decreased; it was normal after fibrinogen infusion. With a modification of the Hellem test the values obtained were slightly decreased. Adrenalin-induced aggregation was absent whereas ADP-and collagen-induced aggregation was near normal or slightly decreased. Thrombofax aggregation was absent in citrated plasma. The abnormalities of platelet aggregation were corrected after fibrinogen infusion or after addition in vitro of fibrinogen, hemofilia A plasma and PPP obtained from an afibrinogenemic patient after fibrinogen infusion. The abnormalities of platelet aggregation were corrected well by ADP, collagen and Thrombofax in heparinized blood, but only a slight correction of adrenalin-induced aggregation was noted. Thrombin aggregation proved to be normal with the higher concentrations, whereas it was defective with the lower ones. Ristocetin aggregation was normal in citrated plasma at the concentration of 1.5 mg per ml but it was absent at the lower concentration (1.0 mg per ml). Ristocetin aggregation was, on the other hand absent in heparinized blood regardless of the concentration. These findings are in agreement with the presence of a prolonged bleeding time in congenital afibrinogenemia and suggest that fibrinogen plays an important role in platelet aggregation and adhesiveness.

Platelet aggregation by various inductors was studied in citrated and heparinized plasma of the following groups of subjects: Normal, hemophilia A, combined factor V and factor VIII deficiency, v. Willeprand's disease and congenital afibrinognemia. The results may be summarized as follows: A-platelet aggregation in citrated plasm 1) platelet aggregation by common inductors ADP, adrenalin and collagen was normal in all groups of subjects but for the patients with congential afibrinogenemia in whom adrenalin induced aggregation was absent or markedly refuced whereas ADP and collagen gave slightly reduced or near normal aggregation curves. 2) platelet aggregation by ristocetin was normal in all groups of subjects but for v. Willebrand's disease in which it was absent. B-platelet aggregation in heparized plasma. 1) platelet aggregation by common inductors resulted to be normal in all groups of subjects except in congenital afibrinogenemia. In this latter case the pattern was still mildly defective but here was an increased aggregation as compared to citrated plasma. These findings have been interpretemmon inductors. 2) platelet aggregation by ristocetin resulted to be absent in all groups of subjects investigated. The possible mechanism of action of the inhibitory effect exercised py heparin with regard to restocetin is discussed.

Platelet aggregation to common inductors and to Ristocetin, Thrombo-fax and Ionophore is normal in congenital factor X deficiency and in factor X Friuli coagulation disorder. Washed normal platelets resuspended in the patient’s plasma and in adsorbed normal plasma showed a normal aggregation. On the contrary, normal platelets resuspended in normal serum failed to aggregate. These studies indicate that factor X plays no role in normal platelet aggregation.

Ellagic acid solutions, regardless of the concentration, failed to alter platelet aggregation induced by ADP, Adrenalin, Collagen, Thrombofax and Ristocetin in normal and in factor XII deficient plasma. A moderate inhibition was noted after addition of ADP both in normal and in factor XII deficient plasma but this was present also in the control systems and was therefore due to the buffer-dextrose solution and not to ellagic acid. These data indicate that Hageman factor plays on role in platelet aggregation.

Platelet aggregation in citrated and heparinized plasma by ionophore A 23187 and Ristocetin was studied in normal subjects and in patients with von Willebrand’s disease and congenital afíbrinogenemia. Aggregation by ionophore was normal in all groups both in citrated and heparinized plasma. Aggregation by Ristocetin in citrated plasma was normal in congenital afibrinogenemia, in normal subjects and in types II and III of von Willebrand’s disease. It was absent in classical von Willebrand’s disease, type I. In heparinized plasma it was absent in all groups, except in some patients with von Willebrand’s disease, type III. It is concluded that ionophore A 23187 behaves in a different way than Ristocetin and has no diagnostic implications.