In the guinea pig, the cochlear‐microphonic potentials and the summating potential (SP) have been simultaneously recorded by means of micropipettes located inside the scala media of each turn of the cochlea. The polarity of the SP recorded in the first turn is negative for the high frequencies (i.e., 6000 Hz) at low levels of sound pressure. For the lower frequencies (i.e., 900 Hz), the SP is recorded positive before it becomes negative. The lower the frequency, the greater the SPL (sound‐pressure level) required to produce a negative SP in the first turn. The SPL at which the SP for low frequencies becomes negative is lower the greater the distance from the oval window. The SP magnitude is linearly dependent upon the logarithm of the duration of sound within the range of values investigated from 40 msec to 2 sec. The amplitude of the negative SP rose monotonically as the intensity of the stimulus was increased, and the neighboring areas of the basilar membrane contributed to the production of the SP. Increase in duration of stimulation increased the amplitude of the SP without bringing into activity new areas of basilar membrane.