Temporal intervals as short as a few milliseconds between 2 brief sounds allow a listener to report that there are 2 sounds, instead of one. A longer separation time of between 15 and 20 msec is required for the listener to report correctly which of the 2 sounds precedes the other. This minimum temporal interval appears to be independent of the kinds of sounds used: whether short or long, of high or low frequency, of narrow or wide band width. There is some suggestion that rise-time and duration may change this minimum interval. The length of the required temporal interval suggests that the judgment of order requires other mechanisms than those associated with the peripheral auditory system.