Abstract: A method for manufacturing a multi-layered hemodialyzer comprises the step of forming a pack of flattened tubular membranes and supporting members therefor, inserting the pack into a box like open-side enclosure to form a dialyzer assembly while positioning inserts in the open side of the enclosure, sealing the open ends of the membranes and the end spaces between the membranes and the supporting members, removing the inserts from the enclosure to leave communication orifices between the inside of the membranes and the outside of the dialyzer assembly, and securing, to the open sides of the enclosure, closing members defining manifold spaces communicating, through the orifices, with the inside of the membranes. In the formed multi-layered hemodialyzer the manifold spaces have a communication port for communicating with the space defined within the membranes the space of which is substantially equal to the surface area of sealing means being occupied by the communication apertures.