A plasma treatment that renders asymmetric polysulfone membranes permanently hydrophilic is reported. Our modification strategy entails treating these membranes downstream from an inductively coupled rf plasma source. Contact angle measurements confirm that the membranes are completely wettable with water as a result of H2O plasma treatment. Mon importantly, the. hydrophilic modification is permanent as plasma-treated membranes remain wettable for more than 16 months after plasma treatment. This treatment achieves the desired change in wettability for microporous as well as ultrafiltration polysulfone membranes, illustrating the universality of this method. XPS analysis of treated membranes demonstrates this dramatic change in wettability is a result of chemical changes in the membrane induced by plasma treatment. Moreover, the membrane modification is complete as the plasma penetrates the thickness of the membrane, thereby modifying the entire membrane cross-section.