Abstract: A hypodermic syringe has a tubular body extending along and centered on an axis and having at an axial front end a small-diameter collar formed with a front radially outwardly open seat and, axially spaced backward therefrom, a rear radially outwardly open seat. An end piece provided with a deformable plug fittable sealingly in the collar is adapted to receive a needle. Mounting fingers extending axially back from the end piece have rear ends that engage in a front position of the end piece in the front seat and in a rear position of the end piece in the rear seat. The fingers are of such an axial length that the plug is fitted snugly into the collar in the rear position but is not snugly fitted in the collar in the front position. When the end piece is in the front position a medicament in the body can be lyophilized and when in the rear position the syringe is plugged.