An external functional means for coupling to a blood treatment apparatus designed as a dialysis apparatus for extracorporeal dialysis treatment of blood guided along an extracorporeal circuit in a blood treatment method using a double-needle access to a patient, the functional means comprising: at least one housing body; at least one chamber (9, 15, 21, 57) integrated into the housing body for receiving medical fluids; at least one channel (17, 19, 49) integrated into the housing body for receiving and/or guiding one of the medical fluids; and at least two valve means (35, 36, 39, 40, 47, 51, 53, 61) totally or partially integrated into the housing body for controlling or regulating a fluid from the medical fluids flowing through the external functional means in use, the valve means (35, 36, 39, 40, 47, 51, 53, 61) including a pre-dilution addition valve and a post-dilution addition valve, wherein the external functional means is provided on at least one of its surfaces with a cover means being part of at least one of the integrated valve means (35, 36, 39, 40, 47, 51, 53, 61), and wherein the cover means is connected, in at least one section, to the housing body by frictional and/or by form closure and/or by material connection, wherein the external functional means is designed as a cassette for extracorporeal dialysis treatment of blood, as one of the medical fluids, by means of the blood treatment apparatus, the functional means comprising two pump tube segments (88,90), wherein one of the pump tube segments (88, 90) serves for its insertion into a peristaltic blood pump for conveying blood along the extracorporeal circuit, the other serving for its insertion into a peristaltic substitute pump for conveying substitute as one of the medical fluids, wherein the external functional means comprises a connector for blood to exit from the external functional means and a connector for blood to enter the external functional means, wherein the connectors (11, 13) are connected to the pump tube segment for insertion into the blood pump, wherein the external functional means comprises a substitute addition point through which substitute is introduced and fed through the pre-dilution addition valve and/or the post-dilution addition valve into the extracorporeal circuit when the external functional means is in use. at least one housing body; at least one chamber (9, 15, 21, 57) integrated into the housing body for receiving medical fluids; at least one channel (17, 19, 49) integrated into the housing body for receiving and/or guiding one of the medical fluids; and at least two valve means (35, 36, 39, 40, 47, 51, 53, 61) totally or partially integrated into the housing body for controlling or regulating a fluid from the medical fluids flowing through the external functional means in use, the valve means (35, 36, 39, 40, 47, 51, 53, 61) including a pre-dilution addition valve and a post-dilution addition valve, wherein the external functional means is provided on at least one of its surfaces with a cover means being part of at least one of the integrated valve means (35, 36, 39, 40, 47, 51, 53, 61), and wherein the cover means is connected, in at least one section, to the housing body by frictional and/or by form closure and/or by material connection, wherein the external functional means is designed as a cassette for extracorporeal dialysis treatment of blood, as one of the medical fluids, by means of the blood treatment apparatus, the functional means comprising two pump tube segments (88,90), wherein one of the pump tube segments (88, 90) serves for its insertion into a peristaltic blood pump for conveying blood along the extracorporeal circuit, the other serving for its insertion into a peristaltic substitute pump for conveying substitute as one of the medical fluids, wherein the external functional means comprises a connector for blood to exit from the external functional means and a connector for blood to enter the external functional means, wherein the connectors (11, 13) are connected to the pump tube segment for insertion into the blood pump, wherein the external functional means comprises a substitute addition point through which substitute is introduced and fed through the pre-dilution addition valve and/or the post-dilution addition valve into the extracorporeal circuit when the external functional means is in use.