In this paper we present a low-energy ion scattering (LEIS) study of the site exchange of Fe adatoms with Ag atoms from the Ag(100) surface. The time-of-flight (TOF) spectra obtained at low temperatures have been interpreted with a newly developed LEIS simulation program MATCH. After low temperature deposition (˜50 K) of Fe atoms oil the Ag(100) surface, the Fe atoms occupy adatom positions. These Fe adatoms exchange sites with Ag atoms from the first layer, starting at a temperature of 130(10) K.