  The needs of various accelerator and space projects stimulated recent
developments to the MARS Monte Carlo code. One of the essential parts of those
is heavy ion ionization energy loss. This paper describes an implementation of
several corrections to dE/dx in order to take into account the deviations from
the Bethe theory at low and high energies as well as the effect of a finite
nuclear size at ultra-relativistic energies. Special attention is paid to the
transition energy region where the onset of the effect of a finite nuclear size
is observed. Comparisons with experimental data and NIST data are presented.
