A surgical stapling apparatus, comprising: a first jaw member having a lockout assembly including a pivotable latch, the first jaw member including a recess; a drive member "D" having a working end which supports a knife and is movable from a retracted to an advanced position, the knife having an upper flange for engaging the first jaw member and for engagement by the latch, the latch being biased toward the recess in the first jaw member; a cartridge configured to selectively couple to the first jaw member, the cartridge having fasteners and a sled for driving the fasteners from the cartridge when the drive member is moved to the advanced position, the cartridge having a blocking member at a proximal end thereof for covering the recess when the cartridge is coupled to the first jaw member and to allow the drive member to move during firing; and a second jaw member having an anvil with staple forming depressions; said latch of the first jaw member further comprising a body portion and an elongate member with a protruberance for engaging the recess and configured to engage the flange when engaged with the recess; whereby in a loaded configuration, blocking member is positioned over recess in contact with the protuberance so as to prevent their engagement with the recess prior to the sled and drive member being fired; and wherein advancement of the working end translates the flange distally to contact the sled which moves blocking member out of contact with the protruberance thereby enabling engagement of the protruberance with recess; and wherein, subsequent to stapling and severing tissue, the working end is moved proximally and returned to a fully retracted position causing flange of knife to contact body portion preventing protuberance from engaging recess and latch to prevent forward movement of the knife until the apparatus is loaded with an unused cartridge. a first jaw member having a lockout assembly including a pivotable latch, the first jaw member including a recess; a drive member "D" having a working end which supports a knife and is movable from a retracted to an advanced position, the knife having an upper flange for engaging the first jaw member and for engagement by the latch, the latch being biased toward the recess in the first jaw member; a cartridge configured to selectively couple to the first jaw member, the cartridge having fasteners and a sled for driving the fasteners from the cartridge when the drive member is moved to the advanced position, the cartridge having a blocking member at a proximal end thereof for covering the recess when the cartridge is coupled to the first jaw member and to allow the drive member to move during firing; and a second jaw member having an anvil with staple forming depressions; said latch of the first jaw member further comprising a body portion and an elongate member with a protruberance for engaging the recess and configured to engage the flange when engaged with the recess; whereby in a loaded configuration, blocking member is positioned over recess in contact with the protuberance so as to prevent their engagement with the recess prior to the sled and drive member being fired; and wherein advancement of the working end translates the flange distally to contact the sled which moves blocking member out of contact with the protruberance thereby enabling engagement of the protruberance with recess; and wherein, subsequent to stapling and severing tissue, the working end is moved proximally and returned to a fully retracted position causing flange of knife to contact body portion preventing protuberance from engaging recess and latch to prevent forward movement of the knife until the apparatus is loaded with an unused cartridge.