Abstract: A syringe unit arranged for a single-use only. The syringe unit comprises a barrel substantially closed at one end by a nozzle and open at the other end. A plunger having a piston is received in the barrel and is movable therealong. A fluid chamber is defined within the barrel between the piston and the nozzle. A syringe needle is releasably secured to the barrel with the cannula extending outwardly from the barrel and communicating with the fluid chamber and is releasable upon rotation relative to the barrel. An engaging means is provided for releasably engaging the piston with the needle whereby when so engaged the piston can be rotated to effect release of the needle from the barrel and then retracted to move the needle into a protective position within the barrel. The engaging means comprises a socket defined in a cavity provided in the needle, and a projection provided on the piston for reception in the socket and engagement therewith.