Abstract A method is described for continuously monitoring local cerebral blood flow by recording pulsatile electrical impedance changes with a sensitive ac bridge and electroencephalograph. An in vitro calibration of the system is presented. Blood flow was measured by the impedance method in several brain areas of anesthetized and unanesthetized cats subjected to various physiological and pharmacological alterations to demonstrate the validity of the method. Separation of cerebral from systemic circulatory changes and the effects of known cerebral vasoconstrictors and dilators were demonstrated. Differential effects of certain drugs on blood flow in different brain areas were detected by this method.