Abstract: Immunoassay and methods for using fluorescent chelates of lanthanide metal ions in conjunction with immunoreactive bodies to permit fluorescent assay in liquid or dry samples. The assay reagent comprises a residue of an immunoreactive body linked to a residue of a protein or polypeptide. The protein or polypeptide is labeled by substitution with a ligand forming a fluorescent chelate with lanthanide metal ion such as europium. The reagent when used in an immunoassay, binds to the immobilized immunoreactive body and excess is washed away. The sample can be dried for later analysis by a suitable fluoremeter.