a large group of procedures which exploit the ability of antibodies to recognise specific antigens. Either the antibody or antigen can be identified with radioactive, fluorescent or chemiluminescent labels and often the reaction is linked to an enzyme system to amplify or modify the effect, moodus, kus aine kontsentratsiooni või hulga määramiseks kasutatakse antigeen-antikeha reaktsiooni (nt. radioimmuunanalüüs)