A container containing a concentrate for dialysis includes a pouch or cartridge containing a solid concentrate of constituents for the dialysis solution, the pouch or cartridge being closed by a connector having a filling channel extending completely through the connector, which is for filling the pouch or cartridge with the solid concentrate, means for introducing a solution-forming liquid into the pouch or cartridge and for extracting the solution obtained, these introduction and extraction means having at least one connecting portion for connecting them to a corresponding port of the dialysis machine. The filling channel is closed by a stopper which has a reservoir containing a second constituent or group of constituents for the dialysis solution, and means for producing an outlet opening in the reservoir contacting the inside of the reservoir with the side of the stopper located in the container.
