The syringe is intended for one-off use and has a syringe barrel (1), a barrel stopper (12) which can be displaced in the syringe barrel (1) by means of a plunger rod (11) and a needle unit (25) accommodated in the syringe barrel (1). The plunger rod (11) and the needle unit (25) are connected to one another by coupling means (20, 40) in order to retract the needle unit (25) into the syringe barrel (1) after the injection. As proposed by the invention, the needle unit (25) comprises a needle holder (26) made from plastic surrounding an injection needle (27) made from stainless steel along part of its length, which is closed off from an interior of the syringe barrel (1) containing an injection solution (50) by means of a seal insert (36) made from pharmaceutical rubber through the injection needle (27) extends from the rear end. As a result of this feature, an injection solution (50) contained in the syringe is in contact exclusively with permitted materials and the syringe can therefore be stored pre-filled.