SummaryA new family with congenital dysfibrinogenemia without bleeding tendency has been discovered in Nancy. Identical laboratory abnormalities were found in the mother and son plasma: prolongation of thrombin and reptilase clotting time.The abnormal fibrinogen affects, only a little, the normal plasma fibrinoformation.The functional characterization of the defect is localized in fibrin monomer aggregation. The release of fibrinopeptides is normal.The abnormal fibrinogen showsa) an alteration in glucidic moiety of the molecule with a high level of sialic acid,b) an disturbance of chromatography on D. E. A. E. cellulose andc) of the electrophoretic mobility.