We tried to detect minimal stimulation-induced glutamate overflow from the surface of a hippocampal slice using an outside-out patch electrode excised from pyramidal cell membranes. The amplitude of the stimulation-induced patch current was dependent on the distance between the slice surface and the tip of patch sensor. The current-voltage relations of the stimulation-induced patch current were similar to those of the current evoked puff by application of L-glutamate to the patch. This indicates that the stimulation-induced patch current was produced by glutamate released from presynaptic terminals, and thus this technique may be useful in the study of transmitter release evoked by minimal electrical stimulation in brain slices.