Cross flow filtration cartridges are made using semipermeable membrane of sheet formation that was cast upon an integral polymeric fibrous support material which exhibits excellent permeate flow in the plane thereof and serves as both backing material and permeate carrier. A fibrous support having a thickness between about 0.4 mm and about 2 mm and at least one surface region with a mean pore size no greater than about 300 microns has a semipermeable membrane cast in situ thereupon from a liquid solution. After gelling to form a polymeric semipermeable membrane, the product is spirally wound about a porous tube in association with feed-passageway-providing sheet material, but in the absence of any separate permeate carrier, to form an effective cross-flow filtration cartridge wherein the feed flow may be spiral and the permeate discharge through one of the side edges.