The effects of iontophoretically applied norepinephrine (NE) on the dentate gyrus field potential evoked by perforant path stimulation were examined. NE potentiated the population spike by 20-400%, whereas the population EPSP was rarely increased. At 39% of the potentiated sites NE application resulted in long-lasting potentiation (LLP) suggesting a role for NE in long-term hippocampal plasticity.