Abstract: An immunoassay method for the detection or quantitation of an analyte suspected of being in a solution comprising: (a) combining said specimen, a first binding component, insoluble particles, and second binding component labelled with a signal generating material in a solid phase retention and separation apparatus having a sufficient pore size such that said particles are trapped within said filter yet permitting rapid passage of fluid therethrough in such a manner that an immunological reaction occurs if analyte is present in said specimen, resulting in the formation of an immunocomplex of insolublized first binding component:analyte:second labelled binding component on or within said filter means; (b) separating bound from unbound material; and (c) determining the presence and/or amount of signal produced which is correlative with the amount of analyte present in the solution.