X-ray fluorescence (XRF) analysis is used for the determination of thickness and composition of surface layers such as electroplated or evaporated coatings. The composition and thickness data evaluation from X-ray yields is done with the help of computer routines where the main prerequisite consists in an accurate calculation of the X-ray production for any given structur of the layer under consideration. Here the so-called enhancement effect plays an important role. In this paper a considerably simplified fundamental parameter treatment of secondary fluorecsence is derived and applied. It is demonstrated that XRF analysis even may be used for nondestructive depth profiling if the measured X-ray yields are influenced by the depth profile with sufficient sensitivity. In the case of strong interelement effects within the layer this technique may be applied successfully, as shown for FeNi foils as a typical example.