Research into microvariations of fundamental frequency (F₀) of speech (intrinsic and co-intrinsic effects) carried out on a large number of languages has brought to light universal tendencies which raise a number of problems, both from the point of view of perception and from that of production, for the interpretation and modelling of intonation. After a survey of these problems, experimental data for French are presented, concerning the intrinsic fundamental frequency (IF₀) of oral and nasal vowels and the co-intrinsic effect (CF₀) of consonants on the onset and pitch point of the F₀ of the following stressed vowels. It is shown that despite considerable intersubject variation, IF₀ differences between the classes of close, open and nasal vowels are significant in both prosodic contexts analysed, but that variations within these classes were not significant (except for the nasal vowels). The principal source of variation for the co-intrinsic effect (as has been observed in many languages) was the opposition voiced/voiceless for the preceding consonant. This effect was greater at the onset of the vowel (4 STs) than at the pitch point where it was comparable to the IF₀ effect (1 ST). A relative independence of the IF₀ and CF₀ effects was noted which tend either to combine or to cancel each other out depending on the phonetic context. A preliminary attempt to incorporate these effects into a synthetic model of intonation, by factoring out observed F₀ contours into segmental and suprasegmental components, suggests that unlike IF₀ and CF₀ effects of consonants, which intervene at a fairly late level of phonetic implementation, IF₀ effects of vowels are quite probably programmed at a higher level.