Abstract: The invention concerns a medical syringe comprising a tubular body, in which slides a plunger comprising an opening, the plunger comprising a sealing piece, movable in the plunger and which closes the opening of the syringe before it is used. The assembly is arranged such that, after the syringe has been used, the sealing piece no longer closes the opening permanently, so that the syringe cannot be used again. All the parts of the syringe are designed for being produced by moulding and automatically mounted in series by axial jointing.