Excitation with low temp. helium or helium/water plasma and subsequent exposure to air of polyacrylonitrile (PAN) ultrafiltration membranes was used to hydrophilize the surface of these materials. We analyzed the effectiveness of this approach as a function of plasma operating variables including gas phase compn., plasma power, treatment time, and system pressure. Following the changes in phys. and chem. compn. of the PAN surface resulting from these modifications was a major aspects of this work. Techniques such as the captive bubble contact angle method, ellipsometry, ESCA, and FTIR-ATR were all used. In addn., the formation and lifetime of peroxides during these processes were detd. At low powers (?25 W) and short treatment periods (?30 s), the main chem. conversion of PAN surfaces was simultaneous hydrophilization and stabilization via PAN cyclization. Relatively small water permeability changes were obsd. as a result of such treatment.