Abstract: The invention provides means for measuring the intercranial pressure of a patient. A small sealed capsule is located in a trephined hole in the patient's skull, with its active face in the form of a diaphragm in contact with the dura mater. The capsule includes a small hollow cylindrical permanent magnet slidable for a short distance along a smooth rod and held against a stop by the diaphragm with a pressure proportional to the intercranial pressure of the liquid within the skull. When an alternating magnetic field of sufficient intensity is applied to the magnet by an external wound inductor, it vibrates on and off its stop, producing an audible signal and the current in the inductor, at this point, is proportional to the said intercranial pressure.