This paper describes the modification of 100, 300 and 1000kD regenerated cellulose membranes by atom transfer radical polymerization (ATRP). Surface-initiated ATRP was used to grow poly[poly(ethylene glycol) methacrylate] layers from the membrane pore surfaces. Membrane characterization was done by ATR-FTIR spectroscopy, FE SEM, AFM, and contact angle measurements. Water flux measurements and dextran rejection studies were also conducted with membranes modified for different polymerization times. Water flux decreased monotonically with increasing polymerization times, while the dextran rejection curves shifted to lower molecular weight cutoff values. AFM images collected before and after rejection testing showed no evidence of fouling by dextran adsorption. These findings support our conclusion that ATRP allows the controlled manipulation of membrane pore size. (c) 2007 Elsevier B.V. All rights reserved.