A method is proposed to determinc the number of nearest coordination spheres in which the pres - ence of limiting short-range order is sufficient to produce long-range order. The use of the method is considered with reference to the example of atomic ordering in solid solutions with b.c.c. and f.c.c. structures. It is suggested that a qualitative dependence exists between the kind of orderdisorder phase transition and the relation of short-range and long-range order in the solid solutions involved.