When the conventional tungsten filament in an appearance potential spectrometer was replaced by an oxide coated filament, barium contamination was detected on the iron specimen being examined. The spectrum obtained showed prominent M structure of barium in addition to weak iron L structure. Even after the work function correction is applied, the barium edges are shifted by several eV from the respective energy levels quoted in the literature. This is presumably the effect of chemical binding of the barium atoms on the surface. The iron and the barium spectra showed slight changes in structure when the specimen was heated in situ.