The parathyroid glands are small, oval endocrine glands closely associated with the thyroid gland. The glands regulate serum calcium and phosphate levels via parathyroid hormone (parathormone). Parathyroid hormone raises serum calcium levels by a direct mechanis on the bone increasing the rate of osteoclastic resorption and promoting break down of the bone matrix, by increasing the renal tubular reabsorption of calcium ions and inhibiting the reabsorption of phosphate ions from the glomerular filtrate and finally by promoting the absorption of calcium from the small intestine, involving vitamin D. Parathyroid hormone is the most important regulator of blood calcium levels and is essential to life whereas calcitonin appears only to provide a comple entary mechanis for fine adjustment. Chief cells are the most abundant cells in the parathyroid gland and are responsible for the secretion of parathyroid hormone.This antibody is useful for the immunohistochemical detection of parathyroid hormone which, when used in conjunction with antibodies to thyroglobulin for each suspected parathyroid lesion, is useful for the differentation of parathyroid from  thyroid tissue.