Auger spectroscopy has been used to measure the composition of ion milled GaAs surfaces in ordered and disordered states. Disorder was introduced into GaAs single crystals by implanting Se+ (5×1014/cm2, 100 keV) or Ar+ (5×1016/cm2, 20–100 KeV) ions. Auger composition profiles with 0.5 keV Ar+ ion milling exhibited As-depleted layers that extended to approximately the depth of the implant region. An enhanced Ar concentration was also seen in the disordered region. These results are compared with similar composition changes in GaAs produced by low energy (<5 keV) Ar bombardment. Arsenic depletion in both energy regimes is associated with preferential sputtering from disordered surface layers.