The x-ray contrast material metrizamide is structurally related to 2-deoxyglucose and inhibits brain glucose phosphorylation both in vitro and in vivo. in vivo. In vivo, however, the present autoradiographic study with labeled 2-deoxyglucose revealed a local increase of glucose metabolic rate in an area of direct metrizamide application to the cerebral cortex. The local increase was 137% above the metabolic rate calculated for the contralateral region. Regions outside the application site showed no difference between the glucose metabolic rates of the ipsi- and contralateral hemispheres. Evidence from the literature suggests that metrizamide may stimulate cortical activity by inhibiting acetylcholinesterase.