Dilutional hyponatremia and aurum hypoosmolality are commonly abserved during transure-thral resection of the prostate in association with the systemic absorption of the irrigating solution. To assess these sequential changes following surgery, 26 Patients were studies who unclerwent transurethral resection of the prostate because of prostatic tumors at Pusan National University Hospital, Where 4% Dextrose in Water is Still used as irrigating solution. 0.9% NaCl and furosemide were administered to all 26 patients in the recovery room after surgery. Blood samples were examined for serum electrolytes and osmolality 7efore induction of anesthesia, immediate-postoperatively, and at postoperative 1 hour, 6 hours and 24 hours respectively, The results are as fellows : 1) Of the 26 Patients, 19 Patients shoved abnormalities in serum electrolytes, especially serum sodium, in the immediate postoperative period, while 7 patients showed a slight decrease in serum sodium but within normal limits. Mean changes in serum sodium was 10.9 mEq/l in the immediate postoperative period, but after administration of 0.9% NaCl and furosemide, the level of serum sodium returned to normal limits within 1~3 hours. Serum calcium decreased approximately 0.8 mg/dl but returned to normal levels 3 hoers after surgery. But no symptoms of hyponatremia or hypocalcemia were not observed. 2) Serum osmolality decreased to about 8.4 mOsm/kg below the preoperative level in accordiance with hyponatremia, but returned to normal bevels 24 hours postoperatively. 3) Blood glucose levels increased about 231.5 mg% but returned to normal levels 24 hours postoperatively.