The purpose of the research reported here was to find out some acoustical and perceptual characteristics of the French nasal vowels. Acoustic analysis was made using a Pole-Zero Analysis-by-Synthesis procedure : below 4 kHz (in the case of male adult informants) the main acoustic correlates of the nasal vowels are the formant shifts and the introduction of two pole-zero pairs, one below F1, the other between F2 and F3. By means of a pole-zero synthesizer, synthetic stimuli were generated : two of them have the spectral characteristics of the real vowels [

] and [

], while the others are stimuli whose spectral characteristics are between those of [

] and [

]. Phonemic and phonetic perceptual tests were conducted. Their results show that formant shifts and pole-zero separation contribute almost equally to the decision on the phonemic identity of /

/ versus /

/, whereas pole-zero separation has a stronger effect than formant shifts in the phonetic judgment on nasality.