Various studies on ion‐beam mixing suggest that the extent of mixing is sensitive to the sign and magnitude of the heat of mixing, ΔHm. This implies a role, not only for random motion, but also for chemical driving forces of the type where the total diffusion flux is modified by the factor [1−αi(1−αi) 2hmp/RT(1+p)]. Here α1 is the atomic fraction of component i, αi(1−αi)hm is the heat of mixing of a regular solution, and p is the ratio of the diffusivities for chemically guided defect motion to those for random motion of all types. The parameter p has never been evaluated for any system and we wish to evaluate it first by analyzing the profiling experiments of Marton, Fine, and Chambers on multilayers of Ni‐Ag. We then obtain further values of p from ion‐beam mixing experiments on bilayers and multilayers. It is shown that it is possible to understand a variety of experimental results relating to profiling and to ion‐beam mixing in terms of chemical driving forces and, moreover, to do so without invoking thermal spikes.