new method of simultaneous determination of composition and mass thickness of alloy films has been developed. It uses the matrix effect correction by the fundamental parameters method and is performed automatically on a computer by the lama program. Only pure element bulk standards are required and no prior knowledge of the thickness of the specimen is necessary. The iteration method is described, and the results are compared with those of electron microprobe, interferometry, and atomic absorption spectroscopy. The method is rapid, nondestructive, and has an accuracy similar to the above methods. © 1977, American Chemical Society. All rights reserved.