A retracting syringe of one use has a plunger comprising a handle portion and a needle retention portion forward of the handle portion. A positive locking structure in the syringe barrel ensures the syringe is not reused. In one embodiment, the positive locking structure is a stop in the syringe barrel. The handle portion separates after one use and is removed from the syringe. In a second embodiment, the handle portion has a plurality of stepped serrations and the positive locking structure is a clip which is movable with respect to both the handle portion and the barrel. In a third embodiment, the positive locking structure is a clip fixed in an enlarged back opening of the barrel with springing points which are protected from a plurality of stepped serrations on the handle portion by a sliding collar. This one use feature can be applied to a nonretracting syringe.
