an agglutination immunoassay method and apparatus therefor in which there are conducted the steps of contacting , in a container , a test sample suspected of containing a desired analyte and a reagent comprising sensitized magnetic - material containing particles capable of reacting with and binding to a desired analyte ; precipitating the particles on the bottom of the container by the application of magnetic force ; allowing the container to stand at an inclination so as to cause the particles to flow along the bottom of the container to form a developed pattern of the particles ; obtaining a representative length of the developed pattern of the particles by an imaging device ; and detecting the presence or absence of an immune reaction from the representative length of the pattern of the particles which has flowed from the bottom of the container , thereby detecting the presence or absence of the desired analyte in the test sample .