Ultratiltration biofunctional membranes with "self-cleaning" ability are described in this paper. Porous asymmetric membranes were formed by phase inversion method followed by the surface modification. Chloromethylated poly(phenylene oxide) served as the precursor. It was aminated by 1,2-diaminoethane to give the anchor sites for papain immobilization. The self-cleaning phenomenon was demonstrated in concentration of casein solutions. (c) 2005 Elsevier Inc. All rights reserved.