Help in diagnosis and disease monitoring requires more and more tests with fast results: To satisfy these requirements, two approaches are possible: full automation and rapid data processing, and multiple simultaneous assays. Simultaneous assays are already commercially available with different kinds of labels (radioisotopes, enzymes, fluorophores, etc). First applications concerned simultaneous determinations of two analytes (eg FSH-LH) by two different radioisotopic (125I, 57Co), or fluorescent (Eu = Sm ...) labels. Recently, assays were described which permit simultaneous determination of more than ten analytes (membrane immunoprinting). Techniques can be classified in three groups: i) one reaction site and a single kind of signal; ii) several reaction sites and one kind of signal; iii) several reaction sites and several kinds of signal. Main applications concern antibodies, antigens and haptens determination. Simultaneous assays will be soon associated with new solid phases and detection modes in fully integrated systems, leading to simultaneous multiple determinations in a single drop of blood.