This monoclonal antibody has been tested in ELISA and Western Blot and reacts specifically with phosphothreonine and shows minimal reactivity by ELISA, and competitive ELISA, with phosphoserine or phosphotyrosine. The antibody reacts with free phosphothreonine, phosphothreonine conjugated to carriers such as thyroglobulin or BSA, as well as phosphothreonine in proteins of both unstimulated and stimulated cell lysates. Although not tested, this antibody is likely functional in RIA, flow cytometry, immunohistochemistry and immunoprecipitation. Phosphorylation of threonine residues is associated with many growth factors and oncogene protein kinases and is important for cell signaling in activation, proliferation and differentiation.