PHOSPHOLIPID bilayers are an important part of biological membranes1,2 and consequently their physicochemical properties have been the subject of intense investigation. There has been much discussion about how similar the properties of phospholipid bilayers are to those of membranes3-5. Because of the importance of ion transport across membranes (such as in action potentials), the question of the similarities of the intrinsic ion permeability and conductance has been raised. However, reliable information on these properties of the unmodified bilayer is scarce and the situation is confused. Here we present, for the first time, accurate sodium and chloride ion permeability measurements across both charged and uncharged unmodified phospholipid bilayers.