A method of potting the ends of a bundle of hollow fibers positioned in a casing is provided, for example, in the manufacture of hollow fiber artificial kidneys. The bundle is inserted into the casing through an open end thereof and the casing ends are enclosed with sealed casing closure member means. The casing ends are spun, while curable liquid sealant is inserted through side apertures in the casing. Accordingly, the liquid sealant migrates by the centrifugal force of the spinning to the interior sealed ends of the casing. After the liquid sealant has cured, the closure member means, sealant, and hollow fibers are cut through at each casing end to expose the bores of the hollow fibers. Alternatively, the closure means can be removed prior to the cutting step.