Using membrane transport characterization and imaging analysis, we describe a series of studies that indicate that ethanol exposure permanently alters the ultrastructural morphology and the transport properties of FAN-PVC hollow fiber membranes (HFM). In particular, hydropermeability and solute diffusive permeability of ethanol treated sample groups displayed significant increases when compared to that of the untreated controls. Atomic force microscopic analysis revealed significant changes in the morphology of the permselective layer following HFM exposure to ethanol. The results call into question the mechanism by which cell encapsulation HFM confer immune protection when utilized in various transplantation sites in vivo.