We have developed a new method for taking continuous measurements of rCBF by means of continuous infusion of 81mKr. Using this method, it is possible to follow the sequential changes in blood flow of various brain regions continuously. The method makes it possible to observe the sequential changes in CBF following drug administration, motor activation and various kinds of stimulation, and, furthermore, to observe the CO2 reactivity and autoregulation of cerebral vessels. It will undoubtedly prove useful in the investigation of various pathological states.