Postoperative phosphate dynamics were studied in 30 patients who underwent radical surgery for thoracic esophageal cancer and who were postoperatively nourished by total parenteral nutrition. There was a significant fall in the serum phosphate level on the 2nd and 3rd postoperative days in all patients. Postoperative hypophosphatemia was due to an increase in urinary phosphate excretion which was indicated by the fall in TRP% and TmPO4/GFR. A highly significant positive correlation was observed between the increase in urinary phosphate loss and the enhanced secretion of parathyroid hormone which was possibly triggered by surgical stress, a decrease in the serum level of calcium, the action of phosphate buffer or diuretics. All the patients except for those with postoperative pulmonary complications responded to the drop in serum phosphate by renal conservation of phosphate. A slight decrease in the serum level of phosphate was also found on the 6th postoperative day in most patients who were receiving parenteral hyperalimentation. The second fall in phosphate was due to transcellular shifts of phosphate. It is concluded that patients with postoperative pulmonary complications develop severe hypophosphatemia which should be prevented by replacement therapy with phosphate in the immediate postoperative period.