A procedure was considered for determining theoretical expressions of the area under the first radial distribution function (RDF) peak, and of the relative co-ordination numbers, n(ij) which depend on the co-ordination hypotheses and on the numbers of bonds between elements of a single type of pair. In this method, two important facts were taken into account. First, the products of atomic factors are functions of s (the scattering vector module) and so they cannot always be considered constant; they were therefore approximated by polynomic functions which best fitted the results obtained from the atomic factors given in international tables. Secondly, consideration of the influence of the structural hypotheses (co-ordinations, existence of certain types of bond) on the area and co-ordination numbers mentioned enabled the most probable local order to be postulated. In order to test the reliability of this method, the method was applied to a set of alloys, quoted in the literature, and the theoretical results obtained agreed very satisfactorily with the experimental values.