Experiments were performed to test whether a change made in the duration of one segment in a naturally produced sentence should be compensated in an adjacent segment if the sentence is to remain temporally fluent. The results showed that compensation is required between some pairs of segments, but not between other pairs, depending on where the two segments occur with respect to word and syllable boundaries. The results suggest that the perception of timing in natural speech is based on events at the syllabic level rather than at the segmental level, and that it is important to maintain the rhythm of the sentence, as defined by the onsets of vowels (especially stressed vowels), if the sentence is to sound temporally fluent.