The principles and use of fluorescent labels in immunoassay are reviewed. Comparison is made with radio- and chemiluminescent immunoassays. Possible fluorescent labels are listed. The following types of assay are described: separation fluoroimmunoassay, immunofluorometric assay, fluorescence enhancement and fluorescence quenching assay, fluorescence polarization immunoassay, fluorescence energy transfer immunoassay, fluorescence protection immunoassay, alternative binding immunoassay, release fluoroimmunoassay and time-resolved fluorimetry and phosphorimetry.