SummaryWhen Inulin is injected in the amniotic cavity, it does never appear either in the mother’s blood or in the fœtus blood. In the same way, when Inulin is introduced in the mother’s circulation, it does not appear immediatly in the amniotic fluid.After some delay, some Inulin is found in the fœtal blood, because the normal fœtus a certain amount of amniotic fluid ; when Inulin is present in this fluid it may be absorbed by the small bowel. Inulin is then excreted by the kidney of the fœtus and is returned by miction into the amniotic fluid. Only, during delivery does Inulin pass through the plancentalwall.Precise data have been collected concerning the rate of Inulin diffusion in the amniotic fluid. It has been proved that the amniotic fluid is not a filtrate either of the maternal or foetal blood. Evidence has been given of a fœtal renal excretion, with spontaneous intra-amniotic mictions. The existence of a third circulation between monozygotic twins has been demonstrated. Increase of the placental permeability during the delivery has been supported. Experiments have given a measurement of the volume of amniotic fluid, of the amount of amniotic fluid ingested by the fœtus in a given time. Furthermore, a pathognomonic sign of fœtal death has been added. It is suggested that this method might give in theîuture the possibility of estimating the volume of the extracellular fœtal fluid.