The brain is the highly organized organ which attributes to consciousness, memory and language. Approximately 85ml of oxygenated blood from the heart is delivered to the brain each minute. In human beings, a steady cerebral blood flow is maintained which cerebral structures are perfused roughly in proportion to their metabolic demands which are actively depend on function. Therefore, cerebral function is the most important physiologic regulator of cerebral blood flow. The measurement of cerebral blood flow is a very important toolin exploring the function of the human brain in healthand disease. An impairment of normal cerebral blood flow indicates clinical derangement of central neruous system. Besides the clinical sympatoms, cerebral blood flow investigation has become our main guideline for judging the timing of operation and prognosis of disease as well as evaluation of treatment. The determination of normal cerebral blood flow in Korean seemed to be enormously important for further study on this subject. For the purpose of establishing normal value of cerebral blood flow in Korean, the author have studied 93 healthy persons with 133Xe-inhalation method using Obrist's two compartmental analysis. Followings were the results. 1) Normal values of FI, ISI, and WIin children below the age of 9 were 113.5+/-36.9, 62.5+/-13.0 and 55.6+/-6.4 each. 2) Normal values of FI, ISI, and WI in the group above the age of 9 were 75.5+/-15.5, 44.6+/-5.7 and 43.1+/-3.95 each. 3) There was no significant difference between mean values of right and left side hemisphere. 4) There was significant decrease in r-CBF in the group above the age of 9, but the decrement by age since after the age of 9 was not significant statistically. 5) The difference of mean values among each lobe was not significant statistically.