THE NOVEL CONJUGATES ARE PREPARED BY USING BIFUNCTIONAL MOLECULES AS LINKING AGENTS. THE CONJUGATES WHICH SURVIVE THE COUPLING PROCESS CAN BE USED FOR DETECTING AND DETERMINING QUANTITATIVELT VERY SMALL QUANTITIES OF ANTI-PROTEIN ANTIBODIES. QUANTITIES AS LITTLE AS 0.2 TO 2.0 NANOGRAMS PER MILLILITER OF ANTISERUM CAN BE DETACTED. INSULIN-BACTERIOPHAGE CONJUGATE WAS INACTIVATED TO A SIGNIFICANT EXTENT BY SERA OF DIABETIC PATIENTS WHO HAS RECEIVED INJECTIONS OF INSULIN, WHICH WAS DILUTED A HUNDRED TO TEN-THOUSAND FOLD. THE INACTIVATION OF PROTEIN-BACTERIOPHAGE CONJUGATES BY THE CORRESPONDING ANTI-PROTEIN CAN BE INHIBITED BY THE ADDITION OF PREDETERMINED QUANTITIES OF THE SAID PROTEIN AND THIS INHIBITION CAN BE USED FOR THE DETERMINATION OF VERY SMALL QUANTITIES OF THE PROTEIN.