Abstract: The invention concerns a novel dialyser cartridge comprising a flat membrane tube through which blood to be dialysed may be passed, membrane support material over the outer surfaces of the membrane tube, a split core between which a central portion of the membrane tube and membrane support material is located and about which core said membrane tube and membrane support material are outwardly spirally wound so that the free ends of the membrane tube and membrane support material are situated at the outer periphery of the winding, a hollow cylindrically walled casing encasing the split core and spirally wound membrane tube and membrane support material, blood inlet means for connection to an arterial line and blood outlet means for connection to a blood venous line leading through the circumferential wall of the casing into the ends of the membrane tube, and a pair of end covers fixed to the ends of the hollow cylindrical casing, one end cover having a dialysate inlet for connection to a dialysate supply line a