The variation of the pressure in the cisterna magna after raising or lowering the arterial pressure, has been recorded in dogs. When the systemic arterial pressure is low (under 50 mm Hg in the carotid artery), the pulsations of the CSF present a morphology of the arterial type. When, on the other hand, the arterial pressure is high (above 200 mm Hg) the morphology of the cisternal pulsations is of the venous or mixed type. The detailed studies of these morphologies are now under way. The other circulatory or respiratory parameters (venous pressure, pCO2) cannot be evaluated in these experiments.