A pneumatic retractable syringe has a plunger (48) having an interior retraction lumen. The plunger and syringe barrel (43) have cooperating locking elements (70) so that the plunger is locked after use within the syringe barrel. After injection of medicament is completed, the needle is retracted into the lumen by compressed gas that is released from a gas cell (25) within the syringe when the gas cell is ruptured just before the plunger reaches the end of its downstream path of travel.
