In order to study the diffusion behaviour of caesium and silver in the technical high-temperature alloys Nimocast 713 LC, Nimonic 86, Inconel 625 and TZM, corresponding samples with polished surfaces were vacuum annealed between 700 and 1050° C for times between 170 and 5500 hr at Cs and Ag partial pressures of 10−6 mm Hg respectively. Post-exposure ion-microprobe mass analysis (IMMA) of a series of such samples, resulted in layer-stripping by sputtering and multielement depth profiles. The data were interpreted quantitatively with a physical model called the local thermodynamic equilibrium (LTE) model, and in some cases with the aid ofγ-spectroscopy with use of radioactive tracing materials. The results are discussed in terms of a comparison between the two approaches, and the quantitative concentration profiles are being used in a study of the diffusion behaviour in such systems. Good agreement with existing Cs diffusion data in pure nickel or molybdenum has been achieved.