Abstract: An automatic sliding door operator for a door mounted upon a door frame for sliding movement in a vertical plane between opened and closed positions includes a drive cylinder to open and close the door by means of a drive piston slideably movable within the drive cylinder between fluid inlets located at each end of the cylinder. Control means are provided to couple a first fluid inlet of the drive cylinder through a controlled source of fluid pressure and to exhaust the opposite fluid inlet continuously throughout an opening stroke of the door and for connecting the second fluid inlet to the source of fluid pressure and exhausting the first fluid inlet continuously throughout a closing stroke of the door. The closing and opening rates of the door is controlled by suitable exhaust metering means continuously metering the exhaust flow of fluid.