The effect of the heat of mixing, ΔHm, on the ion beam mixing of marker systems was studied. The matrices for tne experiment were Mo and Ru, and marker atoms were Ti, Cr, Mn, Ni, Hf, Ta, Pt, and Au. These markers and matrices have heat of mixing ranging from +65 to -227 kJ/mol. Irradiations were done with 300 keV Kr at 77 and 300 K, with room temperature backscattering spectrometry analysis. There was no correlation between the mixing results and heat of mixing, which is consistent with the idea of ion beam mixing of dilute marker system.