Abstract: The invention concerns a procedure for measurement of the material quantities in coating layers applied upon a base material, by utilizing x-ray radiation. The procedure is particularly suited for use in a paper or cardboard manufacturing process wherein onto a material web in continuous motion are applied by steps one or several coating courses. The radiation source and detector are both placed on one side of the moving web, and the procedure is based on measurement of the fluorescence radiation excited by the primary x-ray radiation obtained from the radiation source in the material underlying the coating layer that is to be measured. The primary and secondary radiation both are thereby compelled to pass through the coating layer under measurement before the arrival of the fluorescence radiation at the detector.