This study examines the effect of treatment of defective glassy polymer membranes with a variety of vapors and liquids which have varying solvency power for the Polymer. The pure-ps oxygen/nitrogen selectivities of defective, asymmetric membranes are shown to be permanently increased, in special cases, by treatment with certain solvents which have adequate solvency power to cause a critical level of swelling in the membrane skin layer. Three distinct types of membranes have been treated; asymmetric polysulfone membranes formed by dry/wet phase inversion, spin-coated poly (phenylene oxide)-ceramic composite membranes and solution-deposited polyimide-ceramic composite membranes. While the detailed fundamental processes controlling the elimination of surface defects are complex, our results suggest that plasticization of the selective skin layer, coupled with surface-tension driven cohesive forces are likely to be the key factors at play.