A single injection of cocaine increases extracellular glutamate in the rat dorsolateral striatum 1 day after the acute cocaine was administered (McKee and Meshul, 2005). However, the nuclei that facilitate this increase in striatal glutamate remain unknown. We hypothesized that the cocaine-induced increase in striatal glutamate was produced by activation of the ventromedial (VM) nucleus of the thalamus via the thalamo-corticostriatal or thalamostriatal pathways. First, rats received an electrolytic lesion of the VM. One day after a single cocaine or vehicle injection, extracellular glutamate was measured in the dorsolateral striatum using in vivo microdialysis. The motor thalamus lesion blocked the cocaine-induced increase in striatal glutamate and reduced extracellular glutamate to the level of the vehicle-treated group. This study shows a critical role for the VM nucleus of the thalamus in mediating the effects of cocaine on extracellular glutamate levels in the rat dorsolateral striatum. Synapse 64:445–448, 2010. © 2010 Wiley-Liss, Inc.