PURPOSE: To enable exact and easy measurement by using the fixed phase carrier of antimonoclonal PIVKA-II in the stage of measuring PIVKA-II (prothrombin precursor material and said material of which the degree of carboxylation of the residual group of the glutamic acid thereof is incomplete).

CONSTITUTION: PIVKA-II is extracted from the blood plasma of a person who takes warfarin and after refining, the PIVKA-II is dosed to a mouse and the spleen cells are extracted. Antimonoclonal PIVKA-II antibody is obtd. by a cell fusion method. The antibody is fixed to the well of a microtiter plate for an enzyme immunoassay. A specified amt. of the test blood plasma and suitable enzyme labeled antihuman prothrombin antibody, for example, antihuman prothrombin rabbit IgG are brought into reaction with said well and thereafter the activity of the labeling enzyme bound to the fixed carrier is determined by measuring the density of the coloring by the enzyme substrate and the coloring reagent and is contrasted with the calibration curve obtd. preliminarily with the known PIVK-II, by which the PIVKA-II is exactly and accurately measured. The method and reagent are thus utilized for eartly location of the hemorrhagic disease owing to lack of vitamin K, etc.