Research in detecting regional changes in brain metabolism related to functional activity is reviewed and supplemented by original results from positron emission tomography (PET) and the 18F-fluorodeoxyglucose method (FDG). A formula for calculating the value of local cerebral glucose metabolism (LCMRGlc) is discussed. Results concerning auditory stimulation suggest that metabolic responses are determined by the stimulus content and analysis strategy used by the subject rather than the side of stimulation. Tactile stimulation of the hand and fingers caused asymmetrical increases in LCMRGlc confirming topographic maps of the postcentral gyrus and other functional studies. Data from visually stimulated normal subjects show how the visual hemifields project to the opposite calcarine cortex. Studies of patients with hemianopsia or various field defects demonstrated that metabolic scanning can reveal alterations of cortical function not detectable by CT scan. Data obtained reveal the ability of metabolic mapping to subdivide the occipital cortex into distinct regions. Such measurements may also anticipate the course of visual recovery. Findings of increased overall right-hemispheric metabolism during the performance of verbal and spatial cognitive tasks are consistent with earlier results from right-handed males. Results for the frontal eye fields provide the first experimental evidence that lateralized metabolic activity, produced by cognitive tasks, causes similarly lateralized activity within a motor region. It is further demonstrated that FDG is able to provide information on such states as vigilance and anxiety.