The anastomosis surgical stapling instrument is provided with a slide plate within the yoke which is responsive to the movement of the center rod in order to block the movement of safety lock prior to positioning of the anvil assembly in a position for firing of the staples. The slide plate is biased by a spring to follow the movement of the center rod. Further, the center rod is provided with a recessed portion to provide a clearance for the arms of the handles so that jamming of the center rod is avoided after firing of the staples. An indicator is also provided to positively indicate when the staples have been fired. This indicator is mounted in the side of the yoke and is responsive to the movement of the pusher tube.