The effects of midazolam (3 nM) perfusion on the membrane and synaptic properties of dentate gyrus granule neurons were examined in hippocampal slices obtained from young adult (4–6 months) and old (24–26 months) Fischer 344 rats. In young neurons, midazolam perfusion resulted in a hyperpolarization of the resting membrane potential with no apparent change in the input resistance. Midazolam perfusion also produced a significant increase in the amplitude of the post-spike train afterhyperpolarization (AHP). In neurons obtained from old animals, midazolam perfusion also produced a hyperpolarization of the resting membrane potential but did not signficantly change the AHP. These effects may result from altered calcium homeostasis in neurons of the aged brain, and suggest that at least some of the direct actions of benzodiazepines on mammalian central neurons are altered during aging.Key words: aging, midazolam, hippocampus, dentate granule neuron, post-spike train afterhyperpolarization.