PURPOSE: To realize a high sensitivity and quick measurement by covalent- bonding a compound represented by a specified formula and an immunogenic carrier through a carboxyl group and parenterally dosing an animal with an antigen thus produced thereby producing an antibody.

CONSTITUTION: A compound shown by formula II (n is an integer of 0 to 5) is produced by causing reaction between a cyclohexanone derivative and 2- amino-1-cyclopentane-1-carbonitrile in the presence of polyphosphoric acid ethyl and subjecting a compound thus produced to hydrolysis. A protein, polypeptide or sugar protein, is employed as the immunogenic carrier. They are covalent- bonded through a carboxyl group to produce a composite which is employed as an immunogen generating antibody. An animal is dosed by intravenous, hypodermic or intranasal injection. After dosing with a small quantity of antigen, the same antigen is given at a predetermined interval and the whole blood is sampled when the value of antibody in the blood serum is maximized. The whole blood is purified by separating the blood serum and used as an antibody thus measuring the quantity of compound shown by formula I in a sample quickly with high sensitivity.