Sixteen patients suffering from benign intracranial hypertension were studied by a continuous measurement of intraventricular pressure, a simultaneous recording of intraventricular and sagittal sinus pressures, and a measurement of the cerebrospinal fluid (CSF) resistance to drainage. Isotope cisternography was performed and the patency of the dural sinuses verified by direct sinography or phlebography or both. The same procedure was used to study 6 other patients suffering from disorders leading to the same type of intracranial hypertension. In 16, our results confirm a defect in CSF absorption mechanisms linked to an abolition of the pressure gradient between CSF and sagittal sinus in 6 patients, as well as an important increase in CSF resistance to drainage in 10 others. Despite this defect, the CSF circulation was normal in most patients (10 of 12) as demonstrated by isotope cisternography.