TiN and VN single-layers were grown on (100) and (111) MgO substrates as model systems for future studies of V diffusion and understanding the evolution of the lubricous V2O5 phase on coating surfaces. The present study aims at elucidating the epitaxial quality and microstructure of TiN and VN films grown by unbalanced d.c. magnetron sputtering from Ti and V targets in Ar+N-2 on (100) and (111) MgO substrates. X-ray diffraction and electron back-scatter diffraction give evidence for epitaxial growth of the films on both MgO substrate orientations. Transmission electron microscopy studies reveal a cube-on-cube orientation for all film/substrate combinations. The higher dislocation density and larger fraction of misoriented grains for VN films on MgO is explained by the higher growth rate and lattice mismatch compared to TiN. Nanoindentation measurements of the (100) oriented single-crystal films reveal hardness values of similar to 35 GPa for TiN and similar to 23 GPa for VN. (C) 2007 Elsevier B.V. All rights reserved.