The atomic structure of the (100) surface of NiAl was investigated by low-energy ion scattering spectrometry (LEISS) using 1000 eV He+ ions as well as alkali ion impact collision ion scattering spectrometry (ALICISS), using 1450 eV Na+ ions. The ALICISS results were analyzed with a computer program based on a model using hitting probability concepts. The LEISS results showed that the top layer consisted mainly of Al with an Al/Ni ratio of 76/24 and the second layer entirely Ni. The ALICISS results could be best explained by a vertical relaxation of 25% (Delta d(12)=-0.36 Angstrom) between the first and second layers and a relaxation of 15% (Delta d(24)=-0.43 Angstrom) between the second and fourth layers. These results are discussed in terms of published data from the literature.