The authors have tried to ascertain in a preliminary study if monitoring of fetal cerebral blood flow velocity during labour could identify a situation threatening the fetal brain, which could justify a compulsory fetal extraction. Nine patients were explored at term during labour. The Doppler signal was recorded using the abdominal route at the level of the fetal internal carotid. The diastolic carotid index was used (DCI = D/S). In 5 cases, fetal heart rate (FHR) was normal during labour and the DCI was on average comparable for each of the patients and the mean DCI (20.1 ± 1%) was in close agreement with the values normally seen after 33 weeks of amenorrhoea during pregnancy. The case of isolated deceleration shows that deceleration causes an almost instant drop in the telediastolic flux, but the index increases more rapidly than could be expected from the increase in cardiac frequency if this phenomenon were of purely cardiogenic origin. In the case of bradycardia, it was noticed that during the return to the initial FHR frequency, the DCI was much higher than during the measurements performed before bradycardia. In the 1st case of pathological FHR, the index was very high and remained elevated during all the observation period. The fetus presented at birth a normal Apgar score as well as normal blood pH and neurological examination. In the 2nd case of pathological FHR, the FHR was abnormal with decelerations, the DCI increased rapidly and remained high. Suddenly, while the abnormal FHR persisted in its general aspect, deepness and duration of the decelerations, a return of DCI to basic level was noticed over 11 measurements during a 9-min observation period. As shown in animals and newborns, the autoregulation of the brain circulation is suspected in the human fetus without being as yet firmly established. The results reported herein tend to prove its existence. In the last case, the results could perhaps be interpreted as a loss of cerebrovascular autoregulation, the possibilities of cerebrovascular adaptation of the fetus being trespassed. This hypothesis needs further confirmation through another set of observations.