An immunoassay method for conveniently and highly accurately assaying anelastin digestion product in a circulatory fluid of a subject which is usefulin detecting aortic dissection. This method, which comprises immunologicallybinding a first antibody and a second antibody to an elastin digestionproduct, is characterized in that the first antibody and the second antibodyare each an antibody selected from the group consisting of monoclonalantibodies produced by a hybridoma HASG-30 (FERM BP-08489), a hybridoma HASG-2(FERM BP-08488) and a hybridoma HASG-61-1 (FERM BP-08490) and antibodieshaving specificity and affinity for the human aortic elastin digestion productequivalent to any of these monoclonal antibodies.
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