Rocket immunoelectrophoresis was used to determine the fibrin (ogen) degradation products, the appearance of which is one of the important criteria of the fibrinolytic process. Compared with the plasma protamine paracoagulation test, counterelectrophoresis, or Fi and staphylococcal clumping test, this method was more specific, easier to be reproduced, and more accurate quantitatively. There was no false negative or false positive results. This method was considered to be useful in determining whether there is any increase of the fibrinolytic activity.