Surgical fastener applying apparatus

The present disclosure relates to a surgical fastener applying apparatus for applying fasteners to body tissue. The apparatus includes a cartridge receiving half-section defining an elongated channel member configured to releasably receive a firing assembly and a single use loading unit. A lockout structure prevents insertion of the single use loading unit into the channel member after the firing assembly is mounted to the cartridge receiving half-section. Alternatively, the lockout structure prevents full insertion of the firing assembly into the cartridge receiving half-section, if the single use loading unit is not engaged with the firing assembly.