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