The auditory masking effect of a noise burst on a preceding weak stimulus was studied. A short 1000-cycle tone preceded a burst of white noise by a variable silent interval. The threshold intensity level of the tone was taken as a measure of the masking provided by the noise burst. The effects were examined of combinations of the following conditions: tone durations of 5, 10, 15, 20, 25, and 50 msec; silent intervals of 0, 2, 5, 10, 25, and 100 msec. and noise burst levels ranging from 50 to 130 db sound pressure level. Appreciable elevations of tone threshold were observed for silent intervals less than 25 msec. Threshold elevations increased progressively as noise burst level was increased. The latter effect increased with shorter silent intervals. The tone-noise interval was a more critical factor than tone duration.