Abstract: In a syringe, in which a needle assembly is engaged by a plunger and withdrawn into a syringe barrel for safe disposal, the plunger slides in a resilient insert secured at the proximal end of the barrel. The insert engages an annular ridge near the distal end of the plunger when the plunger, with the needle assembly attached to it, is fully withdrawn, thereby securely locking the plunger to the barrel, and reliably preventing distal movement of the plunger after the needle assembly is withdrawn into the interior of the barrel. The part of the plunger that protrudes proximally from the barrel may then be snapped off.