The electrical responses of the cochlea were used to study combination tones as produced through distortion in the ear. Guinea pigs (Cavia cobaya) were stimulated with 2 pure tones under 2 conditions, with a loudspeaker when the ear was intact, and with a mechanical vibrator applied to the head of the stapes after removal of all the more peripheral portions of the middle ear. The pattern of combination tones was similar for these two forms of stimulation. The results thus do not support the assumptions made by Helmholtz and others that there is a significant degree of non-linearity and asymmetry in the movements of the drum and ossicles. Distortion in these structures is not wholly excluded, but it is unimportant in relation to the distortion that appears beyond the stapes. Distortion appears in the action of the hair cells of the organ of Corti.