PURPOSE: To provide the subject monoclonal antibody capable of recognizing the individual specificity of 1st carcinoembryonic antigen used in immunization, usable for the identification of this individual and having restricted use and no generality because of the lack of reactivity with the other carcinoembryonic antigen.

CONSTITUTION: The objective antibody 1 is a monoclonal antibody selected from monoclonal antibodies produced by a hybridoma obtained by the fusion of a myeloma cell with an antibody-producing cell obtained by immunizing with the 1st carcinoembryonic antigen. It is selected and identified as an antibody reactive with this 1st carcinoembryonic antigen and nonreactive with the 2nd carcinoembryonic antigen, normal feces antigen 1, normal feces antigen 2 and nonspecific cross reaction antigen used as selection marker antigens.