To examine the question of whether the distortion product 2fl - fh is unique, whether a special nonlinear mechanism is responsible for its production, estimates of 2fl - fh and of 2f1 + fh amplitudes were obtained in 3 listeners. Threshold shifts measured with a tone-on-tone masking paradigm for each distortion product suggested that each had similar properties and were masked by other tones as if they had a physical realization in the cochlea. Their masking was not a function of stimulus fine-time structure. The 1 dB/dB growth of 2fl - fh was not changed by rendering it inaudible as previously suggested. Possible explanations of the 1 dB/dB growth of 2fl - fh compared with the accelerated growth of 2fl + fh were examined.