The appearance of cold-precipitable fibrinogen (cryofibrinogen, CF) was first reported by Korst and Kratochvil1 in migratory thrombophlebitis associated with carcinoma. Campbell and co-workers 2 studied a patient with purpura and occlusive vascular disease in whose plasma large amounts of the protein were detected. Kalbfleisch and Bird3 demonstrated similar findings in the plasma of patients with prostatic carcinoma and with pulmonary fibrosarcoma. In subsequent studies McKee and his associates 4 detected sizable amounts of the precipitate in the blood of 28 of 650 hospitalized patients. The protein was found to be most frequently associated with metastatic carcinoma, but was also observed in patients with emboli and in collagen disease. Jager 5 made similar observations in a patient with leukemia, in two patients with pneumonia, and in one with scleroderma. Our interest in this subject was aroused by the finding of a large quantity of cryofibrinogen in the plasma of