It is of importance to detect split products derived from fibrinogen or fibrin for the diagnosis and therapy of intravascular proteolysis (digestion of fibrinogen, fibrin, factors V and VIII). A simplified method of detecting the split products was presented by using a tanned red cell hemagglutination inhibition immune assay as in pregnancy test of Pregnosticon or Serotest. The method was easily performed within 2 hours. A minimum sensitivity of fibrinogen concentration to be detected was approximately 5μg per ml. By the application of this test system to gynecological and obstetrical materials, a large amount of the split products was detected in defibrinated plasma or serum samples from the umbilical cord, the uterine cavity during menstruation and patients with obstetrical hypofibrinogenemia.