The renal excretion of inorganic phosphate in intact and in parathyroidectomized dogs was compared using several procedures for varying the filtered phosphate load. Parathyroid deficiency did not consistently modify the adjustment of renal tubular phosphate transport in response to fasting or to phosphate administration. Parathyroid hormone apparently is not involved in the mediation of these adjustments in tubular phosphate transport. Renal retention of phosphate does not appear to be responsible for the fasting hyperphosphatemia which accompanies parathyroid deficiency. Altered removal of inorganic phosphate from the extracellular fluid, presumably by the cells of soft tissues, offers a more reasonable explanation for the elevation in serum phosphate concentration after parathyroidectomy. However, parathyroid deficiency does not modify cellular uptake of phosphate following insulin and glucose administration.