In central and low Franconian dialects of German and Dutch, a lexical tone contrast (accent 1 versus accent 2) exists that is enhanced by a durational difference. While pitch differences vary according to intonation and sentence context, syllables are generally shorter when they have accent 1. In addition, vowels in those syllables are more open, in comparison with vowels in syllables with accent 2. Perception experiments with natural vowels whose acoustic durations had been manipulated revealed that high vowels are perceived as longer by Dutch listeners than midvowels when acoustic durations are equal. It is argued that vowel raising of longer vowels, or vowel lowering of shorter vowels, serves as an enhancement of duration differences. The tendency is widely attested to in the vowel systems of Germanic languages, where short (‘‘lax’’) vowels are opener than long (‘‘tense’’) vowels, and vowel height is used to enhance a phonological duration contrast. In the dialects investigated, vowel height is manipulated to enhance a durational difference, which in turn enhances a tonal contrast. The explanation of the durational illusion of vowel height is the listener’s compensation of the universally shorter duration of higher vowels.