Using a sensitive two-site immunoradiometric assay which detects intact PTH, we studied the kinetics of PTH secretion undergoing unilateral neck exploration and removal of a parathyroid adenoma. Analysis of the rate ot disappearance of PTH indicated a tri-eponential clearance pattern. The early phase had a half-life of 10,8 mn, the second phase had a half-life of 86 mn, the last phase had a half-life of 5 hours.