Abstract: A separatory apparatus for selectively separating components of multi-component fluids in which a multiplicity of contiguous capillary fibers are uniquely arranged and supported within a housing having a non-cylindrically shaped central portion. In the primary application of the device a multicomponent fluid such as blood flows interiorly of the fibers and a dialysate flows externally of the fibers. Embodied proximate the fluid inlet portion of the device is a uniquely configured fluid distribution element which stratigically positions the fibers and directs the flow of the external fluid, or dialysate, uniformly through the passageways defined by the external walls of the fibers. In this way channeling of the fluid is eliminated and a uniform fluid flow along the external surfaces of each fiber is realized. In this way all of the fibers can be effectively used for mass transfer thereby markedly improving the overall efficiency of the device.