We succeeded for the first time in extracting and purifying a coagulation fibrinolysis factor in the placenta, that is, a placental plasminogen activator (PPA). Using the enzyme-labeled antibody technique (indirect method), we investigated the localization of PPA, fibrinogen (FBG) and fibronectin (FN) in the placenta. And we tried to elucidate the physiological significance of the above three. The F(ab')2 fragments of their antibodies were produced by pepsin digestion, because there were various Fc receptors in the placenta. The results are summarized as follows: PPA was produced in the trophoblast, and was secreted out of the microvilli. FBG was located in the plasma. But, in the placenta, it was not in the cells and the connective tissue of which chorionic villi was composed. FN was located in the ground substances of connective tissue in the chorionic villi, and was associated with the cell structure. Because PPA, FBG and FN showed the same distribution on the fibrinoid material, it is expected that coagulation fibrinolysis activity proceeds in that fibrinoid material.