In speech production many acoustic cues are correlated with the presence of a major syntactic boundary. Here the relative contribution of three acoustic cues, fundamental frequency contour, duration, and amplitude to perceptual segmentation process was evaluated. The stimuli were ambiguous algebraic expressions, such as “A times E plus 0,” in which the middle term E could be a member of either the first or the second phrase. Two levels (appropriate and neutral) of each of the three cues were varied in a complete factorial design. The results indicated that while all three cues significantly influenced the placement of a phrase boundary, duration was more potent than either amplitude or the fundamental frequency contour.