Nowadays industrial control systems consist of number of components of several types: sensors and actuators, controllers, man-machine interfaces, database servers, computer networks, etc. Importance of particular units to the overall operation of the system may differ according to their role in the system. Total malfunction of most of the components can be quickly recognized in most cases. However, there exist cases, when for example a hidden fault of a sensor may impact negatively on proper operation of the control system or on the product quality but the fault is revealed with a significant delay. Even more tricky may be a partial degradation of function of a system component: worsening of the overall operation of the control system can be consequently recognized only statistically and it is difficult to reveal its cause. Examples of such situations can be a worn sensor or actuator, overloaded computer resources, unevenly delayed network communication, etc. Of course, there exist number of means for monitoring and fault detection of system components. The project aims at development of a consistent approach to this problem resulting in the advanced probabilistic monitor of a distributed control system. Main features of the solution are: a) Consistent treatment of pervasive uncertainty. Reliability and preciseness of each piece of information which is available in the control system can be considered as uncertain. Calculus of probability can be utilized as measure of the uncertainty. Consistent probabilistic approach will thus enable to evaluate measure of malfunction of a single system component and propagation of its influence within the control system. b) Hierarchical evaluation of control system "health". Utilizing models of relations among particular system components, the approach enables to evaluate the overall control system health. Such "pyramidal" structure enables to express proper operation of the whole system by a single variable and, on the other hand, to trace a trouble down to its source. c) Modularity. Specific type of evaluation of proper operation is assigned to particular types of system components. Applied to sensors, it takes into account physical quantity being measured, electrical properties, type of communication etc. Another method is used for evaluation of proper operation of a network or a computer, to mention a few. Once particular evaluation modules are developed they can be used repeatedly according to the structure of the control system. d) Modelling of inner relations within the control system. Relations among particular components are modeled to evaluate impact of potential malfunction of a component on another one(s). As an example, reliability of output of a single controller which uses inputs from several sensors depends on reliability of particular sensors the weights of which can be considered as parameters of the related model. On the other hand controller reliability also depends on proper function of its hardware, timing, etc., which should be taken into account as well. Due to nowadays ubiquitous effort for decreasing of maintenance costs and improving quality of production, the monitor may be attractive for operators of virtually any industrial control system. To make the accomplishment of the project aims realistic, the project considers an industrial control system of a reasonable extent, for example in the scale of a production line or an array of annealing furnaces. Data from the real control system are utilized for off-line tests and experiments.