The effect of isoflurane anesthesia on local rate of glucose utilization was investigated in the rat brain by means of the autoradiographic14C-2-deoxyglucose method. Local cerebral glucose utilization (LCGU) was measured in 26 neuroanatomic structures of awake and isoflurane-anesthetized rats. Isoflurane anesthesia (1.5% inspired) caused both increases and decreases in LCGU. Significant reductions were found in all cortical areas examined and in primary sensory relay nuclei of central visual and auditory pathways. Among regions of the extrapyramidal motor system, LCGU was increased in substantia nigra pars compacta, and decreased in cerebellum, red nucleus, and ventral thalamus. Large increases in LCGU were observed in some structures of the limbic system such as the medial habenulo-interpeduncular system and the CAsfield of hippocampus. LCGU was significantly reduced by isoflurane in the CA1-CA2field and dentate gyrus of hippocampus. These results are similar to previous findings on the LCGU response to other inhaled and intravenous anesthetics and further confirm the regional specificity of the effects of anesthetics on brain metabolism.