Abstract: A high security receptacle for a key is provided which is attachable to a door or like structure having an interior surface and an exterior surface. The receptacle comprises an elongated cylindrical housing having a length greater than the width of the door and a longitudinally extending cavity formed in the housing and which is open only through one axial end of the housing. The housing is positioned through a like shaped aperture formed through the door so that the open end of the housing faces outwardly from the exterior flush surface of the door while a portion of the housing protrudes radially inwardly from the interior surface of the door. A radially extending flange on the housing is secured to the door and has a surface which flatly abuts against the interior surface of the door and is secured to it by conventional threaded fasteners. A key is positioned within the interior of the cavity and, thereafter, the open end of the cavity is closed by a closure plug.