Abstract: A filter for absorbing proteins in an aqueous solution which is circulated and constrained to flow through the filter includes numerous absorbent units formed of a polymeric material for absorbing the proteins, sand for slowing the rate of flow of the aqueous solution sufficiently to permit the absorbent units to absorb the proteins, and a water-permeable envelope for containing the absorbent units and the sand. The polymeric material is preferably of an open-cell variety and preferably macroporous, cross-linked polystyrene. The sand is preferably common, washed commercial silica. The envelope is formed of a stretch-resistant nylon mesh to minimize the escape of the sand and the absorbent units. The absorbent units preferably have pores, and the pores have diameters of about 60 to 250 Angstroms and the units preferably have a surface area of about 200 to 900 square meters per gram and a porosity of between 0.20 and 0.90 milliliters of pore per milliliter of bead.