Ultrafiltration membranes are largely being applied for macromolecular and heavy metal ion separations from aqueous streams. Cellulose acetate and sulfonated polysulfone-based membranes prepared in the absence and presence of the polymeric additive poly(ethylene. glycol) 600 in various compositions were subjected to the separation of macromolecular proteins such as bovine serum albumin, egg albumin, pepsin, and trypsin. Toxic heavy metal ions such as copper, nickel, cadmium, and zinc were subjected to separation by the blend membranes by complexing them with the polymeric ligand polyethyleneimine. The effect of the polymer blend compositions and additive concentrations on the rejection and permeate flux of both proteins and metal ions is discussed. The separation and permeate flux efficiencies of the blend membranes are compared with those of pure cellulose acetate, sulfonated polysulfone, and polysulfone membranes.