Abstract: Throw-away syringe, of the type constituted by a cylindrical tubular body in which a stopper can be displaced in the direction of its axis being the latter controlled by a manually actuated stem and in the above syringe, between the stopper associated to the stem and the discharge end of the tubular body, is fitted freely a second stopper carrying a blade placed in an adequate setting of said stopper, a blade inoperative during the backward movement of the stopper and operative to make a mark or incision in the advance direction, a mark through which the inner pressure of the cylindrical body is equalled to the atmospheric pressure to prevent sucking out and therefore re-using the syringe after its first use.