Abstract: Hollow fiber fluid fractionation cells such as used in artificial kidney machines are manufactured by placing a series of half sections of the longitudinal walls of the cell on the periphery of a winding wheel; winding fluid-filled permeable hollow fibers thereabout until the section is full or slightly over-full; placing another mating half shell over each fiber-filled section on the wheel and assembling the cell core; cutting the courses between each section and draining the fluid therefrom; putting an initial fluid potting compound about the courses of fibers and centrifugally casting the potting compound about the fibers at each end of the cell; cutting the fibers at each end within the area of the potting compound to re-expose the hollow cores thereof and placing end caps on and affixing them to each end of the cell to complete the assembly of the cell.