Glutamate stimulation of the lateral supramammillary nucleus (SUL) in urethane anaesthetized rats produced a substantial increase in the amplitude of the perforant path-evoked population spike in the dentate gyrus, without affecting the population EPSP slope. One third of the spike enhancements lasted longer than 20 min. These data suggest that SUL afferents provide a mechanism for both short- and long-lasting heterosynaptic modulation of hippocampal throughput.