A surgical stapling apparatus, (100,200) comprising: a housing (102,202); an elongated member (104,204) extending from the housing; a tool assembly supported on a distal end of the elongated member, the tool assembly including a first jaw member and a second jaw member; a cartridge assembly configured to be releasably supported on the first jaw member, the cartridge assembly including an actuation sled; an anvil operably supported on the second jaw member; and a drive member having a working end, characterized in that: the anvil comprises a stop and the apparatus further comprises a spring coupled to an interior surface of the second jaw member, wherein the spring is configured to urge the working end of the drive member to position the working end of the drive member in alignment with the stop on the anvil to prevent the working end of the drive member being advanced distally when the surgical stapling apparatus does not have the cartridge assembly releasably supported on the first jaw, or when the cartridge assembly releasably supported on the first jaw is spent; the actuation sled comprises at least one mechanical interface; and the working end of the drive member comprises at least one mechanical interface, whereby, when the surgical stapling apparatus has the cartridge assembly releasably supported on the first jaw in an initial unused state of the cartridge assembly, the at least one mechanical interface on the actuation sled is positioned to engage the at least one mechanical interface on the working end of the drive member to drive the working end of the drive member out of engagement with the stop against the bias of the spring to allow advancement of the drive member through the tool assembly, and wherein the actuation sled and the cartridge assembly are provided with an indent and a detent that releasably engage to maintain the actuation sled in place while the cartridge assembly is being installed on the first jaw member, the indent being released from the detent when the working end of the drive member contacts the actuation sled during distal advancement of the drive member. a housing (102,202); an elongated member (104,204) extending from the housing; a tool assembly supported on a distal end of the elongated member, the tool assembly including a first jaw member and a second jaw member; a cartridge assembly configured to be releasably supported on the first jaw member, the cartridge assembly including an actuation sled; an anvil operably supported on the second jaw member; and a drive member having a working end, characterized in that: the anvil comprises a stop and the apparatus further comprises a spring coupled to an interior surface of the second jaw member, wherein the spring is configured to urge the working end of the drive member to position the working end of the drive member in alignment with the stop on the anvil to prevent the working end of the drive member being advanced distally when the surgical stapling apparatus does not have the cartridge assembly releasably supported on the first jaw, or when the cartridge assembly releasably supported on the first jaw is spent; the actuation sled comprises at least one mechanical interface; and the working end of the drive member comprises at least one mechanical interface, the anvil comprises a stop and the apparatus further comprises a spring coupled to an interior surface of the second jaw member, wherein the spring is configured to urge the working end of the drive member to position the working end of the drive member in alignment with the stop on the anvil to prevent the working end of the drive member being advanced distally when the surgical stapling apparatus does not have the cartridge assembly releasably supported on the first jaw, or when the cartridge assembly releasably supported on the first jaw is spent; the actuation sled comprises at least one mechanical interface; and the working end of the drive member comprises at least one mechanical interface, whereby, when the surgical stapling apparatus has the cartridge assembly releasably supported on the first jaw in an initial unused state of the cartridge assembly, the at least one mechanical interface on the actuation sled is positioned to engage the at least one mechanical interface on the working end of the drive member to drive the working end of the drive member out of engagement with the stop against the bias of the spring to allow advancement of the drive member through the tool assembly, and wherein the actuation sled and the cartridge assembly are provided with an indent and a detent that releasably engage to maintain the actuation sled in place while the cartridge assembly is being installed on the first jaw member, the indent being released from the detent when the working end of the drive member contacts the actuation sled during distal advancement of the drive member.