We describe the application of Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) to the determination, by depth profiling and imaging analysis, of O-18 tracer diffusion profiles in oxides. Procedures for obtaining high quality profiles from raw SIMS data are given. It is demonstrated that the analysis of extremely short diffusion profiles (20 nm or less) is particularly advantageous with ToF-SIMS. As an example, we resolve the isotope profile for diffusion through a space-charge layer at the surfaced of an Fe-doped SrTiO3 sample. (c) 2005 Elsevier B.V. All righis reserved.