The masking of silent intervals, or gaps, by surrounding noise bursts was investigated. The durations and the spectrum levels of the two noises were varied and the just detectable gap ΔTdetermined. The first experiment demonstrated the conditions in which duration judgments may have provided a cue. The remaining experiments were therefore designed so that this duration cue was not available. The second experiment indicated that changing the second noise duration from 200 to 2 msec did not greatly affect ΔT, suggesting a close relationship between forward masking and gap detection. Finally, Plomp [J. Acoust. Soc. Am. 36, 277–282 (1964)] has argued that a graph of the level of the second noise in decibels as a function of log ΔTtraces the time course of decay of the first noise. If so, the data from the third experiment indicate that this decay rate depends on the spectrum level of the noise but not on its duration.