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We made experiments of the inferior collicular potentials in acoustic and electrical stimulation for the purpose of studying fundamental issues for cochlear implantation. Guinea pigs with normal Preyer's reflex were used for this study. The results were as follows: (1) in acoustic stimulation relatively wide and large waveforms were gained but in electrical stimulation sharp and narrow ones were gained, (2) in acoustic stimulation the input-output curve of latency and amplitude was biphasic but in electrical stimulation it was monophasic. For this reason, in acoustic stimulation by click, when the intensity is low (under 80 dB SPL) stimulus site would be comparatively low frequency fibers. When the intensity is high (over 80 dB SPL) the stimulus site would shift to high frequency fibers. Therefore, many more neighboring fibers start responding. This results in biphasic input-output curves of latecy and amplitude. By electrical stimulation, however, it would be possible to stimulate only a restricted area among the bipolar electrode. Therefore, as the intensity increases, the response amplitude increases and becomes saturated at a constant level. This results in monophasic input-output curves of latency and amplitude.