The metabolic effects of gamma aminobutyric acid (GABA) unilaterally infused for 24 h into the nucleus basalis magnocellularis (NBM) of rats were studied using the 2-deoxyglucose method for measuring local cerebral metabolic rates for glucose (CMRglc). These results demonstrated that GABA infusion at the concentration of 100 micrograms.microliters-1 induced a strong ipsilateral depression in glucose utilization in the NBM and in some surrounding structures (e.g., the lateral hypothalamic area, thalamus, and amygdala) as well as in the major cortical targets of NBM neurons (i.e., the frontal, parietal, and temporal cortices). On an other hand, GABA infusion at the concentration of 10 micrograms.microliter-1 had no significant effect on cerebral metabolism compared to the saline-infused rats. Nevertheless, both GABA at the concentration of 10 micrograms.microliter-1 and saline induced a reduction of cerebral metabolism in the infused NBM, compared to the contralateral noninfused NBM. It was also demonstrated that saline pretreatment reduced the metabolic depression induced by GABA infusion at the highest concentration. When GABA was infused at the concentration of 100 micrograms.microliter-1, a slight reduction of CMRglc was observed in the hemisphere contralateral to the infused one, mainly in NBM target areas. In view of our previous behavioral data, these results suggest among others, that there is no necessary relationship between cerebral glucose metabolism and behavioral expression.