The study of diffusion in thin layers is particularly indispensable in the case of plating Vedal type of sheet-metal. Standard methods of examination are not at all suitable for the study of diffusion in such fine layers. After an analysis of the experimental possibilities, two methods of examination likely to resolve this problem are discussed, one a local spectrographic method, the other using microhardness readings. A detailed description of the two methods is given. The spectrographic method on an oblique section immediately gives the absolute values of the diffused elements, but it is a delicate application. The microhardness readings method is rapid and easy, but it only gives relative values of the concentrations. A comparison of the two methods, made on the same test-piece (Vedal), has nevertheless, revealed the coincidence between the microhardness curve and the concentration curve in the case of copper diffusion in aluminum. So it is the microhardness readings method which is the best one in this case, having regard to rapidity and precision. In other cases, preliminary testing by the local spectrographic method is indispensable.