Abstract: A security ventilating system for an arrangement of coordinated sliding doors comprising one or more lift-out metal grills each constructed to fit between one partially opened door or window and the door or window frame at each of several different openings. For a typical arrangement in which a left-hand door opens by sliding to the right, the left-hand vertical bar of a lift-out grill is secured in a vertical channel fitted to the inside edge of the left vertical channel of the door frame. The right-hand vertical bar and several of the parallel vertical bars of the grill are designed to fasten in alternative open positions to a series of short vertically-aligned channels fastened to the left-hand stile of the partially open door. A centrally disposed horizontal stud fixed to each of the vertical bars at the different ventilation openings is constructed to engage the door handle of the open door.