Depth event-related potentials in humans were studied during a series of simple cognitive tasks. The previously reported finding of large, polarity-reversing potentials in medial temporal lobe (MTL) during tasks which evoke P3 at the scalp was confirmed. Within the latency range of the scalp N2/P3, at least two depth components were identified which are consistent across patients, and topographically distinct. They have task correlates similar to P3 in that they are larger to rare attended tones than to frequent or ignored tones and are present to rare omitted stimuli.