Electro‐acoustic equipment and methods for the study of aural microphonics and action potentials of laboratory animals are described. A new feature is the placement of electrodes not only on the round window but also in one or more very small holes drilled into the cochlea of the guinea pig.Analysis of the aural microphonics so recorded confirm the conclusions of Wever and Lawrence, of Békésy, and others. The microphonics generated at the apex by low tones or near the round window by high tones axe conducted electrically to the other end of the cochlea with an attenuation of at least 10 db. The effects of the local injury caused by the small holes are described, and their relation to anatomical position confirms the earlier data of Stevens, Davis, and Lurie. Detailed comparisons of phase relations, wave form, etc., at different positions did not prove feasible because of electrical leakage of the aural microphonic from one turn to the next through the bony partitions.At high intensities the microphonic for a tone of 3000 c.p.s. or higher may show a very strong “sub‐harmonic” at the apex although the sub‐harmonic component is very small at the round window. The threshold for appearance of the sub‐harmonic is very sharp.