Abstract Intracellular activity was recorded from CA1 neurons in rat hippocampal slices. Iontophoretic application of glutamate produced a fast and reversible depolarization associated with an increase in action potential discharge rate and only minimal conductance changes. Concurrent application of norepinephrine (NE) or isoproterenol with moderate iontophoretic currents or in a microdrop potentiated the depolarizing responses to glutamate. This effect was not reproduced by serotonin. It is suggested that NE acts postsynaptically to increase the efficacy of the depolarizing action of excitatory neurotransmitters.