The aim of the paper is to present the results of testing and validation of a fuzzy expert system, SPARTA II, for advising on spare parts for maintenance of electrical and electromechanical systems. The expert system was examined within a wide-ranging series of tests, which include both precise end vague (fuzzy) data. A conclusion is derived that SPARTA II generates good lists of spare parts stock levels for missions specified by a fixed duration and for infinite tune horizon tasks.