Lewis, Jessica H., Wilson, John H., and Brandon, John M.: Counterelectrophoresis test for molecules immunologically similar to fibrinogen. Am. J. Clin. Pathol. 58: 400–404, 1972. Counterelectrophoresis for 30 min. in agar gel allows detection of fibrinogen or its derivatives, called “molecules immunologically similar to fibrinogen” (MISFI). Antibody to fibrinogen, prepared in rabbits, is a gamma globulin and moves electrophoretically toward the cathode. Fibrinogen is a beta globulin, part of which migrates toward the anode at a pH of 8.2. MISFI are α1 to α2 globulins. The patient materials tested are plasma, “fast” serum, and 2-hr. serum, unheated or after being heated to 56 C. for 5 min. Fast serum is rapidly clotted with thrombin and thromboplastin and contains EACA to prevent lysis. In counterelectrophoresis, paired wells are punched in agar and filled with antibody or patient plasma/serum. A precipitin line formed between the two wells indicates MISFI in serum. Patients with active intravascular clotting have MISFI (which may be stable at 56 C.) in both fast serum and 2-hr. serum. When in vitro fibrinolysis or poor clotting is present there is a line with 2-lir. serum but not with fast serum.