However the osmotherapy in neurosurgical field have to control the intracranial been doing by intravenous in pressure and brain fusion of hypertonic a urea solution, this hypertonic urea solution has some undesirable side effect like rebound rising of pressure, local irritation, hemolysis, hematuria, some changes in ECG and great changes in electrolyte. We had made some clinical and fundamental studies about mannitol that was reported by Wise, B.L. and Chater, N. in 1961, for new osmotherapic agent in neurosurgical field. Mannitol has been administered to 86 patients of intracranial tumor, head injury and other lesion. Our clinical experiences showed the mannitol is a highly useful and most safe agent for reducing intracranial pressure and brain bulk. The patients received 15% water solution of mannitol intravenously, with dose of 1 to 4 gm/kg of mannitol and we have administered 500 to 1500 ml of 15% mannitol solution within 30 to 45 minutes. In these cases, the intracranial pressure had lowered to 25 to 85% of initial pressure with return to initial level in 150 to 390 minutes without secondary rebound above initial level. There was usually a correlation between the dosage used and pressure reduction, that is, the larger the amount of mannitol used, the higher the pressure reduction. In 33 cases, mannitol has been given during operation to decrease the brain bulk with great effects. About 90% of the administered mannitol excreated by urine in 12 hrs. The side effects that is reported in patients received urea have not encountered by mannitol infusion.