An injection device for a syringe incorporates a housing (1) for a syringe (29). A needle shroud (15) is captive to the leading end of the housing and is movable before use between extended and retracted positions. A drive member (17) is releasable from a rearward position within the housing to urge the syringe forwards to project its needle (30) beyond the retracted needle shroud (15) and then to express a dose through the needle. Locating members (12) on the housing capture the drive member (17) at its forward position (attained after expressing the dose). The captured drive member (17) is also arranged to block retraction of the needle shroud (15) from its extended position.