The electrocochleography which is measurable to cochlear potentials is a useful method for detection of hearing threshold, for the differential diagnosis of sensorineural hearing loss and for the study of auditory physiology. We have measured the normal value of SP, SP/AP at the round window in 20 healthy guinea pigs as a preliminary study for the differential diagnosis of sensorineural hearing loss. The results were as follows : 1) AN1 threshold : AN1 threshold was significantly decreased as the frequency of stimuli was increased : AN1 thresholds were 53.93±12.41 dB SPL at 0.5 kHz, 46.52±14.30 dB SPL at 1 KHz, 36.30±8.01 dB SPL at 2 kHz, 22.17±13.26 dB SPL at 4 kHz, 17.73±7.30 dB SPL at 8 kHz. 2) Amplitude and latency of AP according to the intensity of stimuli : As the intensities and frequencies of stimuli were increased, the amplitude of AP was significantly increased. The reverse relationship was observed between amplitude and latency of AP. As the frequency of stimuli was increased, the amplitude-latency curve became steeper. 3) SP, AP, SP/AP according to the parameters of stimuli. (1) ISI : The plateau of AP was noted at ISI between 80 msec and 320 msec. (2) The intensity and frequency of stimuli : The SP, SP/AP ratio were significantly increased as the intensity and frequency of stimuli were increased.