Process and device for the mixing of suspensions with possibly different natures and/or compositions in the stable section of a paper machine. In the process, a suspension, particularly of the backwater of the paper machine, is piped in a mixing tube with the main flow direction in the longitudinal direction of the tube, and additional suspensions, with possibly different solid content, are injected. In the device, a mixing device and piping carry the suspension in the stable section of a paper or cardboard machine and blend suspensions with a higher solid content into a first suspension with little or no solid content. The mixing device and piping include a tube, at least one inlet for the first suspension, a plurality of feeds for the higher solid content suspensions to be admixed, and one outlet for the blended suspension, with a new solid content, arranged downstream from a bend in the tube. The mixing tube extends over a plane including sections of the tube upstream and downstream of the bend, and the impeller axis of a downstream pump is perpendicular to this plane.