The actual cause of approximately 70 % of all failures in hydraulic systems is the contamination of oil with particles /1/. Oil filtration is not sufficient in order to avoid the damage due to wear by particle contamination. Even an optimal filter position and maintenance of the filter cannot protect the hydraulic circuit against infiltrating and generating particles which move through the hydraulic circuit and cause damage before they are selected by the filter. Also, the maintenance expenditure concerning fine filtration is often not accepted by the users of hydraulic systems. In order to reduce the damage due to wear by particle-contaminated oil it is necessary to increase the wear-resistance of the applied components, beside an appropriate filtration. Before the wear-resistance of a hydraulic component can be optimized by the application of modern material and / or design measures, detailed knowledge on the wear-behavior is required. In the following, the methods and results of the examinations on the wear-behavior of pressure-compensated pumps and proportional valves are introduced.