Two kinds of regenerated cellulose membranes for hemodialysis were prepared from casting solutions of N-methylmorpholine-N-oxide (NMMO) and cuprammonium (denoted NMMO membranes and cuprammonium membranes, respectively). The concentration of cellulose in the casting solution investigated was 6-8 wt %. The permeation characteristics of both membrane series were compared in terms of the ultrafiltration. rate (UFR) of pure water, the sieving coefficient (SC) of dextran, and the solute permeabilities of urea, creatinine, and vitamin B-12. The UFR and SC of the NMMO membranes were strongly affected by the cellulose concentration of the casting solution, and NMMO was a preferable solvent for the production of cellulose membranes with high performance; the cuprammonium solution gave low-performance membranes. The pore structures of both types of membranes were estimated with the Hagen-Poiseuille law. The results showed that the NMMO membranes had larger pore radius and smaller pore numbers than the cuprammonium membranes. The differences in the membrane pore structures led to the differences in the performance between the two membrane series. (C) 2003 Wiley Periodicals, Inc.