Abstract: A shielded syringe includes a cylindrical syringe barrel having an interior chamber a needle secured at one end of said barrel and a plunger slidably received within the interior chamber A sheath for preventing contact with said needle is provided with the sheath being slidably disposed on said cylindrical syringe barrel and movable therealong from a closed position surrounding said needle to an open position exposing said needle A locking system for releasably locking the sheath in both the open and closed positions, includes a tab disposed on an inside surface of said sheath an elongate strip member having one and thereof secured to said cylindrical syringe barrel and a pair of berms thereon for engaging said tab. A spring is provided for urging said tab against one of said pair of berms when the sheath is in the open position and in the closed position.