Detailed studies of the range and range distribution of Xe133 and Ar41 ions in aluminum have been made over a wide energy region: 0.5–240 kev for Xe; 0.7 kev to 2.25 Mev for Ar. The results agree well with the previous alkali metal ion measurements. The experimental distribution curves consist of an asymmetric peak followed by a point of inflection and an exponential tail. The change in peak shape with increasing energy agrees at least qualitatively with the expected transition from nuclear to electronic stopping. The theoretical range–energy curve of Lindhard and Scharff fits the experimental data quite well over most of the energy region studied, but significant deviations occur at the lower energies.