Abstract: A disposable syringe for medicinal or similar purposes, of the type, which may be used once only. The piston rod is coupled to the piston through a lost-motion connection. The piston and the piston rod are initially positioned one relative to the other such, that they are--as seen in the moving out direction--rigidly coupled. In the end portion of the cylinder turned away from the injection needle means are provided adapted to lock the piston and the piston rod in said rigid coupling position along a part of the suction stroke length corresponding to the length of said cylinder end portion, such that upon initiating the injection stroke a certain lost motion of the piston rod relative to said piston will occur only after the area comprising said locking means has been passed through, said lost motion causing said piston to become in a state, from which a next effective suction stroke is impossible.