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. Thirty patients, classified as ASA ps 2 or 3, were selected randomly and divided them into two groups as follows: Group l(N=15); Not-administrated furosemide(control group) Group 2(N=15); Administrated furosemide(Experimental group) All patients were premedicated with hydroxyzine(1 mg/kg, IM) and were performed continuous epidural anesthesia with 2/ lidocaine(1-1.5 mg/segment). 5% D-sorbitols were used for irrigating solution, and Hartmans solutions were given for maintenance fluid. And fixed the irrigating container to 60 cm in height from symphysis pubis. With the starting of operation, 20 mg furosemide was administrated to experimental group. The blood samples for serum Na+, K+, glucose and BUN were obtained at preoperation, 10 min, 20 min, 30 min after the stating of operation and immediate postoperative period, and serum osmolality and effective osmolality were calculated. The results were as follows: l) The values of sodium concentration of control group were decreased significantly at 10 min, 20 min, 30 min after the starting of operation and immediate postoperative period as compared with the preoperative value(p<0.05). But those of experimental group were not changed significantly. 2) The values of serum osmolality and effective osmolality were decreased significantly at 30 min after the starting of operation and immediate postoperative period as compared with the preoperative value(p<0.05). But those of experimenta1 group were not changed significantly. These results show that the dilutional effect of excessive absorption of irrigating solution might be prevented by using furosemide intraopertively. So we would like to recommend the use of furosemide during TURP, especially in patients with congestive heart failure or renal failure.