Abstract: An immunoassay for measuring the concentration of a ligand contained in a solid-phase complex prepared by immobilizing said ligand, comprising the steps (1) and (2) or the steps (1?) and (2?): (1) contacting a ligand, a first labeled substance binding specifically to said ligand and a second labeled substance binding specifically to said ligand with one another in a solvent to form a complex of said first labeled specifically binding substance, said ligand and said second labeled specifically binding substance; and (2) contacting said complex with carrier solid-phase particles supporting a substance binding specifically to the first marker of said first labeled specifically binding substance to form a solid-phase complex in which said complex and said carrier solid-phase particles are bound to each other by the first marker, or (1?) contacting a ligand, a first labeled substance binding specifically to said ligand and a second labeled substance binding specifically to said first labeled specifically binding s