This study was conducted to assess the impact of systemic ethanol (EOH) on the glutamatergic transmission in the nucleus accumbens (NACC). Extracellular concentrations of glutamate (GLU) in the NACC of freely moving Sprague-Dawley rats were monitored by intracerebral microdialysis. Intraperitoneal injection of EOH at a dose of 2 g/kg significantly decreased basal extracellular GLU by 21%. In addition, administration of the same dose of EOH significantly attenuated 150 mM K+-stimulated GLU release from the NACC by more than 50%. Since K+-stimulated GLU release has been demonstrated to derive largely from nerve terminal depolarization, reductions of K+-evoked GLU release may reflect in part the effect of EOH on the neurotransmitter pool. The present results suggest that EOH may suppress glutamatergic transmission in the NACC by lowering presynaptic GLU release.