Abstract Cryofibrinogen was separated from the plasma of four patients with skin ulcers on the legs. It was identified as a complex of fibrinogen and the cold insoluble globulin based on its sedimentation coefficients, electrophoretic mobilities, thrombin-clottability and amino acid compositions. It formed a solid gel with fibrin strands in a short time at 4°C and readily redissolved at 37°C. The fibrinogen in the fraction was not significantly affected by proteolytic enzymes since its subunits were found to be well retained when examined by SDS polyacrylamide gel electrophoresis. The heat-defibrination at 56°C for 3 min resulted in a loss of gel forming capacity, however, the reconsitution with an equivalent amount of purified human fibrinogen apparently recovered it to a certain extent, but not to the initial level. The sedimentation coefficient of the non-fibrinogen fraction fell between 11 S and 13 S and its estimated molecular weight was 4.4 × 10 5. The amino acid compositions were found to be consistent with those recently reported on the cold insoluble globulin in the normal plasma.