The effects of MgO and SiO2 additive distributions on alumina grain morphology have been characterized using high-resolution imaging secondary ion mass spectrometry (HRI-SIMS). In alumina samples singly-doped with MgO, the concentration of Mg segregated to grain boundaries is independent of grain boundary length for a majority of grain boundaries studied. Mg segregant therefore redistributes from grain boundaries to microstructural sinks, such as pores and/or second phases, during grain coarsening. In samples singly-doped with SiO2, abnormal grain growth develops and the concentration of Si at grain boundaries is also independent of grain boundary length. Redistribution of segregants is again necessary in this case to maintain constant grain boundary composition. Codoping with Mg/ Si> 1 suppresses abnormal grain growth as a result of increased mutual solid solubility of both ions and an associated decrease in grain boundary segregation. Grain growth kinetics for doped aluminas are reconsidered in light of these observations. (C) 2003 Kluwer Academic Publishers.