The invention relates to the adjusting and locking of the position of a guide rail for a movable window pane in a vehicle door. A device, a vehicle door equipped therewith and a tool provided for the adjusting and locking are disclosed. In the vehicle door, a first mounting plate mounted on the rail side and a second mounting plate mounted on the door side are provided, which are connected to one another by screw-fastenable mounting means. One of the mounting plates comprises an engaging element for an eccentric lever, which on rotation brings about a mutual translational displacement of the mounting plates in an adjusting (Y) direction.