In a master's thesis entitled "Expert system for technical diagnostics of selected systems of Zetor tractors" the collected most essential issues concerned systems of expert and of programming. Next, in an outline of the history of the language used for construction of the diagnostics, system was described. In the next stage issues connected with diagnosing were brought up. Most essential element of the work was to create an application being able to conduct the diagnostics of the chosen arrangement of the tractor Zetor. The program is transparent and simple in the service panel of indicator lights and buttons.