The purpose of this study was to prevent the dilutional effect of excessive absorption of irrigating solution by using furosemide intraoperatively during transurethral resection of the prostate. 30 patients, who belonged to physical status II or III of ASA classification, were selected randomly and divided with two groups as follows: G1 (N=15): Not-administrated furosemide (control group) G2 (N=15): Administrated furosemide (Experimental group) All patients were premedicated with Hydroxyzine (1mg/kg, IM) and were performed continuous epidural anesthesia with 2% lidocaine (1-1.5mg/segment). For irrigating solution, 5% D-sorbitol was used and Hartman's solution were given for maintenance fluid and fixed the height of irrigating container to 60 cm from symphysis pubis. With the starting of operation, 20 mg furosemide was administrated to experimental group. The blood samples for the values of Na⁺, K⁺, Glucose and BUN were performed at the periods of preoperation, 10 min, 20 min, 30 min after the starting of operation and immediate postoperation. Based these date, serum osmolality and effective osmolality were calculated. The results were as follows: 1. The sodium concentration of control group was decreased statistically significantly at 10 min, 20 min, 30 min after the starting of operation and immediate postoperative period as comparing with the preoperation value (p<0.05). But that of experimental Group was not changed significantly. 2. The serum osmolality and effective osmolality were decreased statistically significantly at 30 min after the starting of operation and immediate postoperative period as comparing with the preoperation value (p<0.05). But those of experimental group were not changed significantly. These results show that the dilutional effect of excessive absorption of irrigating solution might be prevented by using furosemide intraoperatively. And so we recommend the use of furosemide during TURP, especially in patients with congestive heart failure or renal failure.