There has been a clear progression in assays for the analysis of PTH and its clinical applications. This includes the innovative use of PTH as a point-of-care assay as an intraoperative measure of the success of parathyroid surgery. The rapid PTH assay has served as a model for the development of other rapid hormone assays, such as for adrenocorticotropic hormone,although the clinical usefulness of these other applications is less well established. Knowledge of the circulating forms of PTH continues to progress. Information about the biologic and immunologic activities of these forms will aid in the interpretation and clinical use of current assays and in the development of new assays with improved specificities. The clinical laboratory will continue to play a vital role in providing testing and support for this important mediator of mineral metabolism.