Abstract: The invention provides a security panel release mechanism for a sliding door or window assembly of the type having a pane movable in a frame to an open attitude in which its free edge is spaced from the frame member with which it engages when closed, the opening so exposed being secured by a security panel; characterized in that (1) the security panel is so mounted that it is movable between a closed position in which it is effective to prevent access to the opening and an open position in which the opening is available as an emergency exit, (2) the security panel is normally held in the closed position by lock means retaining the security panel adjacent the pane frame, and (3) the pane is fitted with lock release means normally ineffective so that the pane opening and closing functions are available, but adapted to be rendered operative in an emergency whereby sliding movement of the pane causes its lock release means to render the security panel lock means inoperative to free the security panel for movement