Immunological assay reagents and assay method

An immunological analyzing reagent comprising a composition containing a biotin-conjugated antigen or antibody against a substance to be analyzed, and a composition containing an avidin-conjugated microparticle, wherein the biotin-conjugated antigen or antibody contains an amount of biotin which does not substantially agglutinate with the avidin-conjugated microparticle in the absence of the substance to be analyzed, is disclosed. Further, an immunological analyzing method comprising the steps of: bringing into contact a sample, a biotin-conjugated antigen or antibody against a substance to be analyzed, and an avidin-conjugated microparticle, the biotin-conjugated antigen or antibody containing an amount of biotin which does not agglutinate with the avidin-conjugated microparticle in the absence of the substance to be analyzed; and detecting the degree of aggregation between the avidin-conjugated microparticle, and an immunocomplex formed from the substance to be analyzed and the biotin-conjugated antigen or antibody, is disclosed. According to the immunological analyzing reagent and analyzing method, a procedure in which an antibody or antigen is carried on a latex particle is not necessary; self-aggregation of latex particles does not occur; a precise measurement of the substance to be analyzed may be carried out; and an excellent reactivity the same as or superior to that obtained by the conventional sensitized latex method may be obtained.