Abstract: The present invention provides a method of identifying and isolating a set of monoclonal and polyclonal antibodies for use in immunometric assays for the detection of UCN III peptide, and the development of a two-site immunoassay for UCN III peptide. Monoclonal antibodies (mAb) have been affinity purified and used to develop a two-site immunometric assay comprising a mAb selected from the list comprising 2F7, 4E3, 4D3, 6D1, 1G10, 2E7, 4F3, 4C3, 5E11, 1A9, 4C4, 4B4, 2G7, 2A4, 1B9, 3H11, 5F2, 4G2, and 2E3 used for capture and a polyclonal antibody used for detection. The immunometric assay of the present invention comprise a method to identify and isolate specific antibodies or fragments thereof establishing the presence and/or amount of a UCN III peptide and detecting the specific binding necessary for determining a sample's UCN III peptide level for correlation with a diagnosis wherein the UCN III peptide level is used to determine whether the subject suffers from OSA.