Two pathways for glutamate toxicity have been described, receptor-mediated excitotoxicity and non-receptor mediated oxidative glutamate toxicity. Here, we show that two distinct forms of receptor-mediated primary cortical neuronal death exist, chronic and acute glutamate toxicity, and that these depend on exposure time. In vitro, neuronal sensitivity to chronic glutamate exposure increased as neurons matured and the initial plating medium contributed as well. In immature neurons, high concentrations of glutamate induced neuronal death. The chronic glutamate toxicity was independent of neuronal density, whereas increased density potentiated acute glutamate toxicity. Activation of ionotropic glutamate receptors (iGluRs) contributed to induction of chronic and acute glutamate toxicity at similar rates at DIV14. Inactivation of the metabotropic glutamate receptors (mGluRs) by AIDA increased neuronal sensitivity to chronic glutamate exposure but not to acute exposure. Neuronal death by acute toxicity was much faster than by chronic toxicity in which activation of mGluRs was involved. These results suggest that acute glutamate toxicity is quite different from chronic toxicity, in which activation of mGluRs is associated with resistance to glutamate toxicity.