The dissertation thesis dealt with the assessment of the quality of hydraulic oil and determining the mode of wear of the friction surfaces of Baljer & Zembrod manipulating lines through the information traces in the oils by applying tribotechnical diagnostic. In the first part we focused on the theoretical knowledge in tribotechnical diagnostics. In detail we presented the basic analytical methods and advanced instrumental methods of lubricant analysis, which are carried out in tribotechnical laboratories. In the main part, we presented the assessment of the level of degradation of oils itself. In addition we presented mode of wear of the friction surfaces washed in oil through evaluation of the qualitative and quantitative characteristics of the particles found in the oil. In detail we focused on the application of suitable multivariate statistical methods on the data matrix. The thesis introduced a predictive models, which can sort oils into groups based on the assessment of quality of the oil and the state of the friction couples. The models can be used in research and in solving practical tasks in tribotechnical diagnostics of hydraulic fluids in woodworking equipment. Our results showed that the manipulation lines were greatly thermically stressed, due to inadequate oil and machine maintenance. By correlative integration of all methods used we could determine the real mode of the wear of tribologic nodes of the machine. We determined that excessive bearing wear occurred in one manipulation line, due to critical level of resins found in the oil. The experiment enabled early detection of an undesirable process in the tribological node and implement corrective measures before the machine would break down.