Abstract: A disposable hypodermic syringe is disclosed having a barrel (4), a hub (1) and needle holder (2) locatable on the barrel, a plunger (5) with a piston (13) at one end thereof slideable within the barrel, and an interlockable structure on the plunger and needle holder for interlocking the same one relative to the other so that after use the needle (3) is fully retractable into the syringe barrel (4) to prevent accidental stabbing and risk of infection. The needle holder tube (2) has internal barbs (10) which engage behind a domed head (8) of the plunger (5). During use (suction and injection delivery) the plunger domed head (8) is retained behind a membrane (14) within the piston (13) by similar internal barbs (20) inside the piston (13). Preferably the interconnection between the needle holder (2) and hub (1) is a screw thread and the plunger is rotatable to detach the needle holder (2) and needle from the hub.