An injection device (110) is described having a housing (112) that receives asyringe (114) having a sealed boot (123) that covers its needle (118). A releasablelocking mechanism retains the syringe (114) in its retracted position. A sleeve(119) projects from the exit aperture (128) and can be depressed to release thelocking mechanism. A removable threaded cap (111) closes the housing (112),covers the exit aperture (128) and the sleeve (119), thus preventing the lockingmechanism from being released, and engages the boot (123) on the syringe (114).When the cap (111) is removed, it takes the boot (123) with it, no longer closesthe exit aperture (128) and no longer prevents the locking mechanism from beingreleased. Then, the locking mechanism can be released and the injection cyclebegun.
