The changes in local cerebral glucose utilization (LCGU) and neuronal unit activities in the subthalamic nucleus and its major target structures (the pars reticulata of the substantia nigra, the globus pallidus and the entopeduncular nucleus) following microinjection of a GABAergic antagonist (bicuculline methiodide, 0.08 nmol) or agonist (muscimol, 0.2 nmol) into the subthalamic nucleus were determined. The metabolic effect was assessed by measuring LCGU by quantitative [14C]-2-deoxyglucose autoradiography in ketamine-anaesthetized rats. Bicuculline methiodide induced increased LCGU in the ipsilateral globus pallidus, the entopeduncular nucleus and the substantia nigra pars reticulata. In contrast, muscimol decreased LCGU in these structures. The neuronal activities in the subthalamic nucleus and related structures increased following injection of bicuculline and decreased after injection of muscimol. The changes in LCGU within the structures directly related to the subthalamic nucleus were correlated with the changes in the unit activity either in the subthalamic nucleus and/or its projection structures. However, the amplitude of the relative changes in neuronal unit activity were greater than the changes in LCGU. Nevertheless, the results emphasize the functional role of the subthalamic nucleus as an activating structure within the basal ganglia.