Membranes suitable for microfiltration, ultrafiltration, and dialysis consist of polycation-polyanion complexes prepd. by casting an aq. soln. of CM-cellulose (I) and cellulose sulfate (II) into a film and then treating with a cationic polyelectrolyte. Thus, 2.5% solns. of I with degree of substitution 1.0 and II were mixed in amts. to give I-II ratio 2:1, cast into a 2.0 mm layer on a glass plate, topped with a 2.0 mm layer of 20-5% polyethylenimine soln., dried, removed from the plate, and washed. The resulting membrane had throughput 16.0 L/h-m2 and sepn. efficiency 79.5% when used in a Millipore US cell at 0.2 MPa to sep. a 1 g/L aq. soln. of dextran with mol. wt. 500,000. [on SciFinder (R)]