A speaker structures utterances very clearly by grouping words into phrases. This facilitates the listener’s recovery of the meaning of the utterance and the speaker’s intention. To this purpose, a speaker uses, among other things, suprasegmental cues, such as intonation, pauses and prefinal lengthening of speech sounds. The research described here is concerned with the relationship between the strength of prosodic boundaries in spoken utterances as perceived by untrained listeners (perceptual boundary strength, PBS) and the phonetic cues melodic discontinuity, pause, declination reset and, to a limited extent, prefinal lengthening. The results indicate that untrained listeners can give reliable and usable judgments of PBS and that this is true even if the lexical contents of the utterances is made unrecognizable, thus blocking access to lexical, syntactic, and semantic information. There is a clear relation between PBS and the phonetic cues, the general trend being for PBS values to increase as more phonetic cues are associated with a given word boundary. The experimentally obtained PBS values were also compared with boundaries predicted on the basis of a syntactic and metrical analysis of the material. A high agreement was found between the PBS values found and the theoretically predicted prosodic structure.