Abstract: To permit accuracy presetting of a dose for an injection to be ejected from an ampule (12) containing more fluid medication than the dose requires, a plunger (18) which is telescopically received within a tubular element (77) is movable against the customary piston (17) in the ampule for a distance which depends on the extent of telescopic insertion of the plunger stem (18") within the tubular element (77). This extent can be set by a rotary knob or sleeve (56, 65) which rotates the tubular element with respect to the plunger (18); the plunger and tubular element are coupled together by a steeply pitched spiral thread (76), thereby controlling the extent of projection of the combined injection dosing arrangement of plunger (18) and plunger length setting mechanism (77), and hence controlling the amount of medicinal fluid expelled through an injection needle (16) coupled to the ampule (12) at the end of the injection device.