Abstract: A window panel position regulating means for a vehicle door which will accommodate a doubly irregularly curved window panel and will guide the window panel through the slot at the belt line of the door in such a manner that the width of the belt line slot can be maintained at absolute minimum so as to improve the oveall appearance of the door assembly and the functional rigidity of the assembly. The regulating assembly includes a pair of guide channel members mounted within the door panel cavity at the front edge of the door and a third guide channel member mounted within the door panel cavity at the rear edge of the door. Guide follower members are mounted to the window and guided within the respective guide channel members to thereby guide the window through the belt line slot.