A chamber is provided for a blood treatment system and has at least one space defined by a chamber wall, at least one blood inlet, and at least one inlet for a further fluid, which are connected with the space. Both the at least one blood inlet and the at least one inlet for the further fluid are formed on tube sections that protrude into the space of the chamber. In the operating condition of the chamber the space of the chamber is at least partly filled with blood or with a mixture of blood and either the further fluid or some other fluid. At least one, or preferably both, of the tube sections have a length such that the blood inlet and/or the inlet for the further fluid are located below the blood or fluid level in the chamber.