The threshold of a harmonically related pure‐tone maskee (Me) varies sinusoidally as its phase is shifted relative to a sufficiently intense masker (Mr) when both are simultaneously presented to one ear. This phenomenon can be explained by either of two approaches. One involves the assumptions that (a) there is a summation between waveforms within the cochlea and (b) the threshold measurements are consequences of peak detection. To test this interpretation, six normal listeners traced their thresholds at 1500, 2000, and 2500 Hz in the presence of a 1000‐HzMrat each of five intensities, 50–90 dB (SPL) at 10‐dB intervals. Within each session, the phase was shifted in randomly ordered 60° steps through one complete period (of theMe). When confusions due to a 500‐Hz difference tone are avoided by using a narrow‐band (270–540 Hz) masking noise, no phase effects at 1500 and 2500 Hz are evident. The thresholds for the 2000‐HzMe, however, show the usual phase dependencies at equalMrlevels. These findings are inconsistent with the two‐tone interaction explanation and thus support the interpretation that emphasizes a nonlinear response of the auditory system and direct interference between aural and acoustic harmonics.