Glutamine is present at high concentrations in the extracellular fluid of the brain. It shuttles between glia cells and neurons, and serves as a precursor for both glutamate and gamma-amino butyric acid. Direct actions of glutamine at central neurons are, however, not well understood. Here we showed that L-glutamine (0.5-10 mm) evoked a dose-dependent inward transmembrane current in primarily cultured rat hippocampal neurons. Typical responses were outwardly rectifying and had a reversal potential around 0 mV. The current was partially sensitive towards blockers of ionotropic glutamate receptors and was partially carried by activation of N-methyl-D-aspartate receptors. However, cellular responses to L-glutamine showed clear biophysical and pharmacological differences to L-glutamate-evoked currents. Responses were highly specific for L-glutamine and no responses could be evoked by D-glutamine, L-alanine, L-valine, L-leucine and the system-A-specific agonist alpha-(methylamino)-isobutyric acid. Together, these data indicate that hippocampal neurons can be depolarized by electrogenic effects specific for L-glutamine.