Some questions are raised pertaining to the internal representation of syllable nucleus durations, being part of words produced in isolation. A first question concerns the accuracy with which a syllable nucleus duration may be internally represented. Further questions concern some major prosodic regularities which were discovered in earlier articulatory measurements on Dutch nonsense words. It is asked whether these regularities are part of the internal representation language users have of how words in their language should sound. These questions are studied with a method in which subjects are asked to adjust the duration of one syllable nucleus in a synthesized word according to some internal criterion. It is found that the internal representation of a syllable nucleus duration may be more accurate than the spectrographic measurement of its acoustic correlate. The internal representation of how words should sound appears to be governed by rather strict temporal patterns, of which phonological vowel quantity, stress and position in the word are important determinants.