Abstract: Sectional garage door panels are provided with elongated reinforcing beams secured to the inside surface of the panels by supporting a beam on a panel with spaced apart support brackets secured to the panel and securing the beam to the panels at spaced apart points thereon with mechanical fasteners. The beams are preferably channel shaped and the support brackets each include a beam locating projection for accurately locating the beams on a panel and in engagement with panel reinforcing stiles to facilitate quickly securing the beams to the panel with mechanical fasteners. The panels are erected in a doorway and supported by opposed guide tracks prior to installing the beams on the panel to facilitate handling the panels and the beams during shipment and prior to installation.