Abstract: A single use disposable syringe having a piston axially slidable in a barrel for undergoing a retraction movement to fill the barrel with fluid and a forward movement to discharge the fluid from the barrel. An operating rod projects from the barrel for operating the piston and the rod is operatively connected to the piston with capability of relative axial movement therebetween to approach the piston during its forward movement. A flexible finger has one end connected to the piston or rod and a cutting element is provided on the flexible finger in spaced relation from the connected end thereof and facing the barrel. During retraction movement of the piston, the cutting element is retracted from the barrel whereas during forward travel of the piston and approach of the operating rod towards the piston, a deviation member displaces the flexible finger outwardly to produce cutting of the barrel by the cutting element to render the barrel subsequently unusable.