The parathyroid gland has been causally associated with some forms of hypertension, yet parathyroid hormone (PTH) has been shown to possess hypotensive properties. Recently, we described the presence of a circulating hypertensive factor in spontaneously hypertensive rat (SHR) plasma, the expression of which is associated with a novel cell type in the parathyroid gland. In order to determine whether this hypertensive factor might be produced by the parathyroid gland, the effects of parathyroidectomy and parathyroid transplantation on mean arterial pressure (MAP) and hypertensive factor activity were studied. Parathyroidectomy, but not sham operation, decreased MAP in SHR and resulted in the disappearance of the hypertensive factor from the plasma. Transplantation of SHR parathyroid glands into Sprague-Dawley (SD) rats resulted in an increase in MAP and the appearance of the factor in the plasma, whereas transplantation of SD parathyroid glands into SHR had exactly the opposite effect. SD to SD transplantation had no effect on MAP or hypertensive factor activity. Infusions of PTH gave opposite effects to hypertensive factor infusions. These results suggest that the hypertensive factor is parathyroid gland-dependent but is not PTH. On this basis, we have proposed that the factor be referred to as "Parathyroid Hypertensive Factor," or "PHF."