Recent studies revealed that the electrically-evoked middle latency response(EMLR) is useful for patient selection of the cochlear implantation and evaluation of the temporal lobe lesions. It is known that some anesthetic agents alter the general morphology, amplitude, and latency of the waveforms of the EMLR. The purpose of this investigation was to determine the characteristics of the EMLR in guinea pigs under anesthesia with three commonly using anesthetics, ketamine, ketamine and xylazine mixture and pentothal. The results obtained were as follows. 1) The amplitude and latency were changed with time without altering the threshold regardless of kinds of anesthetic agent. 2) Increasing the electrical stimulation intensity or pulse width and decreasing the pulse rate result in a rise of response amplitude. 3) Most stabilized waveforms with maximal response amplitude were observed by using pulse width over 250 μsec, pulse amplitude over 1,000μA and 5/sec pulse rate. 4) Anesthesia with mixture of ketamine and xylazine might result in unstable responses, especially response amplitude, so a careful experiment and analysis was recommended. 5) Ketamine was not a good anesthetic agent for this study because of its short anesthetic duration. 6) Rather stable waveforms with smaller response amplitude were observed under pentothal anesthesia.