EPMA has been applied to electron beam evaporated and r.f. sputtered layers of about 200 µg/cm2. This includes analysis of trapped argon and oxygen ranging from 0.2 to 10 wt%. For primary electron energies of 5 to 15 keV depth range of X-ray emission may be predicted with an accuracy of ± 10 nm. Errors of quantitative analysis are discussed for various correction models and should not exceed 3.5 %