Sets of synthetic vowel sounds which differed in first-formant frequency, second-formant frequency, and duration were presented to a group of listeners for identification. It was found that listeners' judgments depended on all of these factors. Duration was a relatively more important cue for vowels located in the center of the F1-F2 space where a vowel might more readily be confused with one of its neighbors. The perceived duration of a vowel was found to be biased by the rhythm of the sounds that preceded it. In the case of sounds lying near perceptual boundaries, this was sometimes sufficient to change the identity of the vowel.