This study was performed to investigate the ranges of electrolyte changes during conventional neurosurgical anesthetic management. We selected 20 patients who were operated for brain tumor, intracranial aneurysm and arteriovenous malformation randomly. All patients were received solumedrol preoperatively and managed with hyperventilation (PaCO2: 25-30 torr), solumedrol (1.0 gm), mannitol, furosemide during operation. At 30 and 60 minutes after mannitol infusion, serum electrolytes (Ka+, K+) were checked. The results were as follows: 1) Serum K+ concentration was decreased from 3.96±0.46 mEq/L to 3.63±0.40 mEq/L in 30 minutes after diuretic administration (p<0.01). 2) At 60 minutes after diuretic administration, serum K+ concentration was decreased from 3.96±0.46mEq/L to 3.75±0.37mEq/L (p<0.05) and slightly higher than 30 minutes without statistical significance. 3) Serum Na+ concentration was not significantly changed at 30 and 60 minutes after diuretic administration. In conclusion, frequent evaluation of intraoperative serm electrolytes level should be stressed to prevent distortion of it due to hyperventilation and diuretics in neurosurgical anesthetic management.