A new method for producing pressure variations in the pneumatic system of the human ear under control is described, i.e. the mastoid puncture technique. Several investigations are made; the volume displacement capacity of the normal ear drum, the role of the drum as a middle ear pressure regulator, vacuum effects on hearing and transudation, all these changes arc produced by intra-aural pressure variations under control. The accuracy of the previous methods for indirect determination of the middle tar pressure is analysed.