Immunoassays, assay methods, antibodies and methods of producing antibodies for the detection of fibroblast growth factor-23 (FGF-23). The immunoassay and assay method preferably comprise a non-competitive, sandwich-type assay utilizing a first bound antibody having affinity to a first site of the FGF-23 molecule, and a second, labeled antibody having an affinity for a second site present upon the FGF-23 molecule. The antibodies and methods of generating the same include administering antigenic peptide fragments of the FGF-23 molecule, monitoring the antibody titre produced thereby, extracting and selecting antibodies from the antisera having a specificity for the desired antigenic region of FGF-23, and purifying same. The antibodies may be incorporated into the immunoassay of the present invention or utilized for a variety of assay-type purposes for the detection of FGF-23.