Glutamate mediated excitotoxicity is a major area of experimentation due to the potential for prevention of morbidity and brain damage associated with stroke and brain trauma. We have developed a simple rapid method to study excitotoxicity in primary cortical neuronal cultures using propidium iodide (PI) fluorescence read by a multiwell fluorescence scanner. Transient (25 min) or continuous N-methyl- d-aspartate (NMDA) treatment led to progressive neuronal death over 24 h that was blocked by 1 μM MK-801, 10 μM ifenprodil, and 200 mM ethanol. Results with PI fluorescence were identical to those found using the lactate dehydrogenase (LDH) release and trypan blue staining assays of excitotoxicity. This method provides a simple rapid means to test the effects of drugs during glutamate excitotoxicity and to do accurate time course experiments of delayed neuronal death.