This paper describes the principles to determine the distribution of metal elements in a crystal with an x-ray diffraction method. When the elements have similar atomic numbers, the metal distribution is not determined precisely with a conventional x-ray diffraction method. The precision can be improved if we use the anomalous dispersion effect. To determine the distribution of three kinds of elements we need two sets of diffraction data different in x-ray wavelength using anomalous dispersion effect. The anomalous dipersion method is also effective in determining the position of each element in a metal site.
