The invention relates to a controllable piston valve for a vibration damper in a piston/cylinder arrangement with the following features: a piston valve body which controls the flow cross-section, operated by a control piston embodied as a differential piston, the opposed working surfaces of which are pressurised with the pressure for the piston and annular chamber of the cylinder. The control piston and/or the piston valve body are additionally loaded against the greater effective surface with the pressure from a pressure source. The pressure is generated by the combination of a fluid resistance and a fluid capacity, which is supplied from the pressure in the piston or annular chamber of the cylinder.