Abstract: A dialytic apparatus for single-needle dialysis comprises a first pump in the artery conduit, which first pump in the first phase conveys blood from the patient into the expansion chamber while the vein conduit is shut off. At the same time, the second pump transports blood from the expansion chamber to the dialyzer. This regulation is performed in dependence from the pressure in the vein conduit so that the pressure decrease caused by ultrafiltration is counterbalanced. In the second phase, the first pump stands still and closes the artery conduit while the second pump conveys blood out of the expansion chamber to the dialyzer at a constant rate.