The use of 2-deoxyglucose for the measurement of regional cerebral glucose utilization in both animals and humans has gained widespread application. An attractive aspect of regional brain glucose metabolism is its apparent correlation with functional activity in neurons. Animal experiments suggest that this relationship is altered in brain lesions and that barbiturate anesthesia may be employed in the detection of brain regions where uncoupling of metabolism and neuronal function has occurred. A functional metabolic contrast technique is described that will permit determination of regional metabolism that is specifically attributable to neuronal activity. Areas of potential clinical application are discussed.