A syringe having a barrel and a piston actuated plunger reciprocable therein includes a means for retracting the cannula subsequent to dispensing fluid from the syringe. The plunger is engageable with the forward end wall of the syringe barrel after the fluid is dispensed so that retraction of the plunger causes the end wall to break away from the barrel and retract the cannula attached thereto entirely within the barrel. In this manner, accidental puncture and contamination by the cannula is avoided. A plurality of serrations on the forward end wall and adjacent its juncture with the syringe barrel allows the forward end wall to be broken away after mating surfaces on the forward end wall and the plunger rod are engaged. In a first embodiment, the mating surfaces are threaded so that rotation of the plunger rod is required for engagement. In a second embodiment, rotation is not required since the mating surfaces are in the form of a snap-in annular rib and groove. An annular rib is also provided at the open end of the barrel to prevent unwanted retraction of the plunger from the barrel.