Poly(acrylonitrile-co-vinyl chloride) (PAN/VC) anisotropic membranes were chemically modified with poly(ethylene oxide) (PEG) (5000 and 20,000 g/mol) by one of two aqueous reactions : (a) acid hydrolysis of the nitrile group to a carboxylic acid with which amine-terminated PEO (PEO-NH2) reacted or (b) base reduction of the nitrile group to an amine with which PEO-succinimide (PEO-SC) reacted. Approximately 1.3% of the bulk material was whereas 1.8 modified with PEO-NH2 to 3.5% was modified with PEG-SC as determined by proton nuclear magnetic resonance (H-1 NMR) and attenuated total reflectance Fourier transform infrared (ATR FTIR) spectra. Approximately 50 to 75% less bovine serum albumin (BSA) adsorbed to PEG-grafted single skin fibers than to unmodified PAN/VC. Transport properties of modified and unmodified fibers were compared by passive diffusion, convective nominal molecular weight cutoff, and hydraulic permeability. Neither hydraulic permeability nor nominal molecular weight cutoff of BSA changed appreciably after surface modification with PEG indicating that pore structure was not adversely affected by the chemistry involved in grafting poly(ethylene oxide). However, in the absence of any membrane conditioning, the apparent diffusion of cr-chymotrypsinogen (24,000 g/mol) was enhanced in PEG-grafted PAN/VC fibers possibly as a result of reduced sorption of the permeating protein. In vivo biocompatibility in the brain tissue of rats was judged by histological assessment of the host’s cellular response to fibers implanted for 30 days; biocompatibility of both PAN/VC and PAN/VC-g-PEO was satisfactory but improved slightly with PEG grafting.