A separation reagent of magnetic particle solid-phase second antibody for RIA has been studied. Amine silane modulated magnetic particles were activated using glutaraldehyde and coupled with purified second antibody at different pH values. And the experiment on adsorption of purified second antibody by non-activated magnetic particles at pH 8 was carried out simultaneously. The RIA test demonstrated that the binding percentage of non-activated magnetic particle solid-phase was lower and its stability was less than that of the activated magnetic particle solid-phase . The sensitivity was increased and the correlation coefficient of standard cure was 0.9950 for the activated magnetic particle solid-phase second antibody for CEA RIA. The correlation coefficient of the testing concertration in RIA between separations with liquid-phase and solid-phase was 0.9895. Therefore

it is possible for the magnetic particle solid-phase to be used as a general separation reagent for RIA.