Phospholipid vesicles are commonly used as biomimetics in the investigation of the interaction of various species with cell membranes. In this letter we present a P-31 NMR investigation of a simple vesicle system using a paramagnetic shift reagent to probe the inner and outer layers of the lipid bilayer. Time-dependent changes in the P-31 NMR signal are observed, which differ whether the paramagnetic species is inside or outside the vesicle, and on the choice of buffer solution used. An interpretation of these results is given in terms of the interaction of the paramagnetic shift reagent with the lipids. (C) 2016 Elsevier B.V. All rights reserved.