The terminal illnesses of 2 cases of congenital fibrinopenia are described. Both patients died of pulmonary embolism and the lungs of both showed liquifaction in the infarcted areas. A variety of staining techniques failed to demonstrate fibrin either in the original thrombus or embolus or around the infarct. The behavior of infused fibrinogen showed that neither patient destroyed this material unusually rapidly, indicating that neither had developed an antifibrinogen antibody. In one patient the white cell and platelet counts rose to high levels, and extensive bruising appeared; this myeloproliferative reaction was t ought to be related to her previous splenectomy.