Two similar cases of tonal monaural diplacusis are described. When low‐intensity sinusoids within a certain range are presented, several distinct tones are heard in addition to the tone presented. The effects are focussed at 3610 cps for one subject and at 3155 cps for the other. Pitch‐matching and probe‐tone techniques show that the additional tones correspond to combination tones expected in a normal ear stimulated by two tones, one of which is fixed at one of the above frequencies. Hence some basic instability of the auditory mechanism at these frequencies is indicated for these observers. It is suggested that the defect lies in the “peaking” process of the cochlea, so that an adequate explanation of the phenomena may be of some importance to auditory theory.