An injection device is described having a housing that receives a syringe. Thesyringe isbiased by a return spring from an extended position in which the needleextends from thehousing through an exit aperture to a retracted position in which it does not.A drivespring acts via a drive to advance the syringe from its retracted position toits extendedposition and discharge its contents through the needle and a return spring,brought intoplay when the drive has reached a nominal return position, restores thesyringe to itsretracted position. A releasable locking mechanism retains the syringe in itsretractedposition. A sleeve projects from the exit aperture and can be depressed torelease thelocking mechanism. A trigger has a rest position, in which it engages thedrive, retainingit in a position corresponding to the retracted position of the syringe, and adepressedposition, in which it no longer causes the drive to be so retained. The sleevenormallylocks the trigger in its rest position. However, depression of the sleeve intothe exitaperture, allows the trigger to be depressed. Thereafter, the trigger isretained in its activeposition.
