The masking produced by 2 continuous sinusoids located equidistant in frequency from the signal, a pulsed sinusoid of110 sec, was studied. The 2 sinusoidal maskers were of equal energy. Their separation in frequency Δfwas varied. The main parameter of the experiment was the frequency of the pulsed signal. The results can conveniently be summarized in one graph. Along the abscissa, we plot the frequency separation of the maskers (Δf). Along the ordinate, we plot the intensity of the pulsed signal (Is) needed for some constant level of detectability. As the frequency separation of the maskers increases, the curve descends, indicating the pulsed tone is becoming easier to hear (Is∝1/Δf). For moderate frequency separations (Δf<100 cps), the results are independent of center frequency. For example, essentially the same signal intensity in SPL is needed at 250, 1000, or 4000 cps to overcome the masking produced by 2 continuous tones when these maskers are located 20 cps above and below the frequency of the signal. At much wider frequency separations, the results are dependent on center frequency, and a critical band of a kind may be measured. The width of the “critical band” inferred from this experiment is about the same size as the half‐response points of the curve relating the amplitude of the traveling‐wave envelope to frequency; i.e., the “critical band” is nearly 600 cps wide at 1000 cps. [This work was supported in part by the U. S. Army Signal Corps, the U. S. Air Force ESD Contract AF19(604)‐7459, the Office of Naval Research, and in part by the National Science Foundation (Grant G‐21807).]