We report on Korringa-Kohn-Rostoker Green’s function calculations for the ground-state moments of ultrathin Ni films on Cu~001! and on four monolayers ~ML! Co/Cu~001!. The calculations for Ni/Cu~001! show a slight enhancement of the Ni magnetic moment at the surface but a large reduction of the Ni magnetic moment at the Cu interface. The number of d holes at the surface and interface shows a small reduction. However, for Co/Cu~001! the calculation gave only a slightly decreased interface magnetic moment. For Ni on a ferromagnetic substrate, such as 4 ML Co/Cu~001!, no reduction of the magnetic moment occurs, so that Ni at the interface retains its bulk value. These results are in contradiction with recent experimental results obtained using x-ray magnetic circular dichroism on ferromagnetic Ni films grown epitaxially on ultrathin films of Co. For decreasing film thickness, the number of holes and the magnetic moment show a gradual decrease. A real breakthrough is currently occurring in the field of thin film magnetism, which is stimulated by the technological impact of the discovery of effects such as perpendicular magnetic anisotropy and giant magnetoresistance. Ab initio band structure calculations of monolayer coverages have become very powerful and are considered to give reliable values of the ground-state magnetic moments. Moreover, many experimental techniques have recently been developed, and improved in sensitivity, which give information about the magnetic moments in the monolayer ~ML! limit. Especially, x-ray absorption spectroscopy ~XAS! using circularly polarized radiation, which gives rise to x-ray magnetic circular dichroism ~XMCD!, has proved to be ideal to study the electronic and magnetic properties of materials since the relevant ground-state properties can be determined using powerful sum rules. 1‐4 XAS at the L2,3 edges of 3d transition metals involves the excitation of an electron from the 2 p core level to an unoccupied 3d or 4s valence state. Therefore, it is an element-specific tool that can distinguish between the different contributions of the magnetic constituents, something that is not possible with conventional magnetic measurement methods. In this paper we report on theoretical results obtained with Korringa-Kohn-Rostoker ~KKR! Green’s function calculations which are compared with recent experimental results for the magnetic moments and the number of holes per atom. The KKR calculations give the magnetic moment and number of holes for each layer, whereas XMCD gives average values of these quantities corrected for the sampling depth. XMCD from bulk Ni was first discussed in terms of a relativistic tight-binding model 5 which was able to reproduce the intensity of the white lines and satellite features in XAS, but failed to account for satellite features in XMCD. The final-state configuration 2 p 5 3d 9 in the configuration interaction ~CI! model gives a natural explanation for the occurrence of satellite features in core-level spectroscopies, such as in XAS and x-ray photoemission. The Ni L2,3 XMCD was