Latex agglutination tests have been in use since 1956 to detect a wide range of analytes in the clinical laboratory. When spectrophotometers and nephelometers are used in place of the human eye to detect agglutination, it is possible to measure quantitatively and to develop sensitive particle immunoassays. Latex particles may be build from different organic materials to a desired diameter, and may be functionalized with chemical groups to facilitate attachment of molecules Proteins and other molecules may be passively adsorbed to the latex particles or covalently coupled to functional groups. Some described automated latex agglutination tests have sensitivities of a few picograms of analyte.