Calcium metabolism is regulated by three specific hormones: parathor- mone, calciferol metabolites, and calcitonin. Cyclic AMP also plays an important part in calcium regulation, and its concentration in urine can be taken as a measure of parathyroid function. Methods for quantitative measurement of, e.g. calcium-regulating hormones and vitamin D metabolites as well as of cAMP are absolutely necessary for safe differential diagnosis of diseases of the parathyroid like hypo- and hyperparathyroidism. In this monograph all presently available methods are summarized as to whether they can already be obtained as test kits or are still being tested. Radioimmunoassays for the various peptide fragments such as 53-84, 44-68, 28-48, and 1-34 are described, as are immunochemiluminescence methods and adenylate cyclase bioassays. The same is true for the vitamin D metabolites, where the various assays for calcidiol and calcitriol such as HPLC, protein-binding assay with second antibody separation, and double antibody RIA are de§ scribed. Finally, determination of calcitonin and cAMP is discussed in detail. This is a practically and clinically oriented monograph for working in the fields of internal medicine, endocrinology, and laboratory medicine.