The interdiffusion coefficient of binary alloys is related via the modified Darken equation to the tracer diffusivities of the constituents. The thermodynamic factor Φ entering the Darken equation is expressed in terms of the energetic parameters which describe the ordering process in the binary alloy. Our calculations show the dependence of Φ on the long-range order parameter. These calculations are performed with the energetic parameters extracted from the diffuse X-ray scattering data on FeAl.