This paper explores acoustic and articulatory aspects of regressive vowel-to-vowel assimilation known as vowel harmony (VH) in French. Based on three speakers' renditions of 136 pairs of disyllabic word pairs containing a mid-vowel in the first, and a low or a non-low vowel in the second, syllables of each pair, we examined assimilatory effects of final vowels on the duration and spectral properties of non-final mid-vowels. Results show that /e/ and /o/ have longer duration, and occupy a more peripheral position in two speakers' vowel spaces when followed by a non-low rather than a low vowel. Phonological implications of these findings could be that vocalic contrasts referred to as tense-lax distinction in other languages and varieties of French would allow characterizing the assimilatory behavior of mid vowels of standard French in a uniform way.