The masking characteristics of filtered-random noise and amplitude-modulated noise (40-dB pressure-spectrum level) were studied in a series of four experiments using a masking-level difference paradigm, that is, 500-Hz thresholds in S_oN_o and S_πN_o binaural conditions. In Experiment 1 a filtered noise (200–800 Hz) and an amplitude-modulated noise (425–575 Hz) produced equal thresholds in S_oN_o; for S_πN_o, however, the thresholds in amplitude-modulated noise were 1.6 dB lower than were the thresholds in filtered noise. In Experiment 2 S_oN_o and S_πN₀ thresholds were established in three filtered noise bandwidths (200–800 Hz, 335–685 Hz, and 410–600 Hz) and in the amplitude-modulated noise (425–575 Hz). When the bandwidths of the filteredrandom and amplitude-modulated noises were similar, the SπN_o thresholds were the same but the S_oN_o thresholds were different. Experiments 3 and 4 indicated that with amplitude-modulated noise when the zero amplitude crossings of the tone and the noisecoincided, the S_oN_o, SπN_o, and S_mN_m thresholds were 1.2–2.0 dB higher than were the thresholds when the zero crossings of the tone and noise did not coincide. The data indicate that the masking characteristics of filtered-random noise and amplitudemodulated noise are different. The findings are interpreted as an indication that perceptual phenomena depend on the temporal characteristies as well as the power spectrum of the signal and masker.