Abstract: A syringe with a plunger having a compressible piston at its forward end and a harpoon-shaped member extending forward and away from the piston. The plunger travels within a syringe casing which has locking openings at its rearward end. The harpoon-shaped members has a rearward member which biases two locking lugs outward. The harpoon-shaped member is releasably retained within a cavity in the piston. The plunger includes a pair of channels running along its length as well as a crosspiece positioned within each channel which provides a slot into which the locking lugs are received. Following an injection with the syringe, the piston and harpoon-shaped member are pushed forward into the casing resulting in a compression of the piston and the attachment of the harpoon-shaped member to an inner part of a needle holder. The plunger with attached needle can then be retracted until the two locking lugs snap into the openings formed in the outer casing.