The invention relates to a container containing a concentrate for dialysis, which container comprises: a pouch or a cartridge containing a solid concentrate of constituents of the composition of the dialysis solution, the pouch or the cartridge being closed by a connector provided with a filling channel extending completely through the connector, intended for filling the pouch or the cartridge with the solid concentrate, means for introducing a solution-forming liquid into the pocket or the cartridge and for extracting the solution obtained from the pouch or the cartridge, these introduction and extraction means being provided with at least one connecting portion for connecting them to a corresponding port of the dialysis machine. The container of the invention is characterized in that the filling channel is closed by a stopper equipped with a reservoir containing a second constituent or group of constituents of the composition of the dialysis solution, and means (131) for producing an outlet opening in the reservoir contacting the inside of the reservoir with the side of the stopper located in the container.
