Methods for characterizing the mechanical and mass transfer properties of hollow fibers and the experimental requirements for dealing with fluid boundary resistances are described. Ultrafiltration measurements, diffusive solute transport and the contribution of convective solute transport are examined. Three hollow fibers are evaluated in detail: cellulosic fibers made by Dow Chemical Co. and by Enka Glanzstoff, and polysulfone fibers manufactured by Amicon Corp. All these fibers have mechanical and solute transport properties useful for fabrication into hemodialyzers.