Even though amorphous diamond-like carbon (DLC) coated tools with their low friction and high wear resistance are well established in a wide field of industrial applications, their employment into humid environments is limited. In humid environments hydrogenated DLC-layers show high friction coefficients and low wear resistance. This work is focused on the development of DLC-coating systems with high wear resistance and low frictional coefficients in the humid environment. Using the Physical Vapor Deposition (PVD)-process, different DLC-coating systems have been deposited, in which the layer properties have been designed related to the humidity conditions. Coating parameters, layer microstructure and layer properties have been systematically analyzed with special emphasis on tribological properties. Correlations between layer structure and corresponding wear as well as friction properties have been scrutinized. The results showed that the coatings with a hydrogen-free top layer have the highest wear resistance and best frictional behavior under humid conditions compared to hydrogenated a-C:H-layers. (C) 2007 Elsevier B.V. All rights reserved.