Abstract High energy electron excitation (up to 50 keV) of Auger spectra with high signal-to-background ratios and a low and flat background slope was used to analyse CoSm alloy thin films. The experiments were performed in an ultrahigh vacuum high energy electron diffraction chamber with in situ co-evaporation of the components onto molybdenum substrates at room temperature and at 550°C. The intensity distributions of the secondary electrons were analysed with a cylindrical mirror analyser and detected via a phosphor-multiplier combination using counting techniques and a multichannel analyser for recording. The analysis of overlapping Auger peaks in the alloy spectra was accomplished by computer-aided subtraction of normalized spectra of the single components. The Auger electron spectroscopy (AES) results were compared with quantitative X-ray fluorescence analysis (XFA) of the films. For deposition of the components at constant rates and the substrate at room temperature, the Auger and X-ray compositions agreed fairly well. However, for deposition at substrate temperatures higher than 500°C, the samarium concentrations were substantially lower than that in the vapour beam, but a relative enrichment of samarium near the film surface was found by comparison of the AES and XFA results. The concentration profile of the films is discussed in terms of an initially low samarium condensation coefficient which increases with the codeposition of cobalt and with time.