The effects of aging on the translation of L-glutamate-induced depolarization into hippocampal neuronal firing frequency were studied in vitro. L-glutamate was iontophoretically-applied to the somatic region of extracellularly recorded single units. In none of the three principal hippocampal subfields (fascia dentata, CA3, and CA1) were there any effects of age on neuronal sensitivity to L-glutamate. Because there are pronounced, region-specific age effects on AMPA sensitivity (3), these results are in agreement with the conclusions of other investigators that the depolarization caused by exogenously applied L-glutamate probably exerts its effects through nonsynaptic mechanisms. These mechanisms, however, which lead to powerful depolarization and action potentials in hippocampal cells, are unaffected by age.