This paper presents the preliminary results of an acoustic study, and a review of previous work on vowel harmony in French. It shows that harmony, initially regarded as regular sound change, is considered an optional constraint on the distribution of mid vowels. Acoustic evidence of anticipatory assimilation of pretonic mid vowels to tonic high and low vowels is shown in three speakers' readings of disyllabic words in two dialects. It is argued that vowel-to-vowel assimilation referred to as vowel harmony does exist in French, and likely to extend beyond morphological contexts in which it was previously thought to operate.