Regional cerebral blood flow was measured with (133)Xe injected into the internal carotid artery in 23 cases of brain tumor and 6 cases of the control. Based on Stochastic method and compartmental method, mean regional cerebral blood flow measured 46±4ml/100g/min and a model curve was induced from control cases as yy=2294 exp(-0.1153t)±706 exp(-0.019t). Deviation value of each curve from the model curve was analysed as an index for rCBF of tumor and non-tumor area. Regional cerebral blood flow on the tumor consisted of not only one compartment but also two compartments that abnormal high blood flow of arterio-venous channel accompanied with abnormal low blood flow or ordinary cerebral blood flow, namely intratumoral steal flow existed. On the other hand, patterns of cerebral blood flow were simple on non-tumor areas; high or low blood flow, however, inter-regional inhomogeneity of rCBF was demonstrated as follows. According to rCBF on tumor, three groups were classified to high blood flow group (3 cases of glioblastoma, 2 cases of meningioma, 2 cases of astrocytoma and 2 cases of AVM), low blood flow group (2 cases of glioblastoma, 2 cases of meingioma, 2 cases of metastatic tumor and 3 cases of intracerebral hematoma), and normal blood flow group (each case of glioblastoma, meningioma and AVM). Mean rCBF was 36±8ml/100g/min on non-tumor areas: Perifocal area measured 37±9ml/100g/min and remote area from the tumor measured 36±7ml/100g/min. No difference of mean rCBF between perifocal and remote area presented. However, 10 cases showed relative perifocal hyperemia that rCBF on perifocal area was higher than on remote area. Eight cases showed relative perifocal ischemia that vis-a-vis. Five cases showed no difference between non-tumor areas. In comparison of rCBF on tumor and non-tumor areas, relative focal hyperemia was demonstrated in 16 cases, relative focal ischemia in 4 cases, and relative focal isoremia in 3 cases. While 10 cases out of the 16 cases associated with relative perifocal hyperemia, all out of the 4 cases associated with relative perifocal ischemia. On another point of view, 6 cases out of 10 cases of relative perifocal hyperemia presented high blood flow on the tumor area and 7 cases out of 8 cases of relative perifocal ischemia presented low blood flow on the tumor area. Cerebral blood flow dynamics of brain tumor was basically characterized into two patterns: 1) In cases of high blood flow on the tumor area, rCBF on the non-tumor areas centrofugally decreased according to the distance from the tumor, that may be called intracerebral steal flow. 2) In cases of low blood flow on the tumor areas, centrofugal increase in rCBF on non-tumor areas that may be functioned as pressure difference in the hemisphere due to brain edema.