The nonsimultaneous masking of a sinusoidal signal (2 kHz) produced by a critical‐band noise (200 Hz wide centered at 2 kHz) is reduced by the presence of a suppressor (bandpass noise, 2300–3700 Hz) during the masker interval. The results of various experiments suggest: (1) Suppression is greater in backward masking than in forward masking. (2) The effect of masker intensity on suppression differs in backward and forward masking. (3) If the suppressor is presented to the contralateral ear, suppression is observed in backward masking but not in forward masking. These experimental differences may reflect a fundamental difference in the processes underlying backward and forward masking. (4) The amount of masking decreases with an increase in the duration of the suppressor. It also decreases with an increase in the duration of a reduction in the intensity of the excitor presented alone. However, this change in masking is markedly different for the two conditions; the effect of the suppressor is not simply to reduce the effective level of the excitor. [Research supported by NIH.]