In three experiments, we have attempted to demonstrate the phenomenon of sensitization. We believe that we have succeeded. A brief high-frequency tone was added to a low-frequency carrier at various phases of the low frequency. Classical threshold was shifted up when the stimulus was added between 200° and 360°, and threshold was shifted down between 0° and 180°. This effect was greatest when the low frequency was at −5 dB sensation level (SL). At 20 dB SL the effect was partially obscured by masking.