There have been various reports describing the changes in cerebral blood flow (CBF) in patients with brain tumors using radioactive xenon (Brock et al. 1971; Reulen etal. 1972). However, one main disadvantage of this method is that blood flow of deeply seated tumors may be incorrectly estimated. Computed tomographic measurement of local CBF by xenon enhancement (Xes-CT) was developed to overcome this disadvantage of the conventional isotope method. Xes-CT not only allows quantitative estimation of flow rates as related to CT images, but also permits determination of local partition coefficient (λ)(Drayer et al. 1978; Meyer et al. 1981; Segawa et al. 1983). In the present study, CBF was measured by Xes-CT in patients with malignant tumors. This paper reports our preliminary experience with this method and discusses its clinical usefulness.