Jaw displacement and velocity were measured during the utterance of nonsense syllable phrases. These phrases were phonemically controlled and spoken with predetermined rhythm patterns in normal, whispered and fast speaking conditions. Jaw displacement was measured by a strain gauge transducer, and velocity was extracted by an analog differentiator. Jaw velocity was found to be significantly related to stress level. Three levels of syllabic stress–unstressed, stressed and prominently stressed–were distinguished on the basis of opening jaw velocity into the vowel of the syllable. Moreover, the rhythm pattern formed by the alternation of these stress levels was unaffected by changes in rate or whispering. A systematic rhythm pattern was not observed in the jaw displacement data however, because that signal was very much influenced by non-rhythmic variations in the phrase.