Abstract: A door section for fitting in a sliding door frame is preferably made of plastic, e.g., PVC. The door section contains a built in pet door. The door section is formed by tubular sides and cross members, and has plastic brackets or fittings that press fit within the tubular members and preferably also may be screwed in place, or otherwise fixed in place, e.g., using epoxy, or both screws and epoxy. Alternatively, the corners of the door section may be welded or otherwise fixed together. The door section has brackets on its side edges for hanging or connecting to the inside of the sliding door frame, and the door section may also have a bracket or catch on the other side edge from which the door section connects to the frame. This bracket or catch is for the existing sliding door's lock. Preferably, insulation strips are provided and preferably an H-shaped vertical section may fit on top of the door section and inside the frame for a fit with less play, and for a smoother or cleaner look.