Al-27 NMR has been used to investigate the solubility limit of alumina (alpha-Al2O3) in the fast ion conductor 0.88ZrO(2)-0.12Sc(2)O(3). It is found that approximately 0.6 mol% alumina is retained in the ZrO2/Sc2O3 host lattice and that at higher doping levels the alumina exists in the specimen as a separate alpha-Al2O3 phase. Further Al-27 NMR evidence is presented to support a view that the incorporated Al replaces Sc in the cubic zirconia-scandia structure. (C) 2004 Elsevier B.V. All rights reserved.