Abstract. Testing complex manufacturing systems, like ASML lithographic machines (ASML 2005), can take up to 45% of the total development time of a system. This test time can be reduced by choosing wisely which test cases must be performed in which sequence, without making investments in test cases or the system. With the test sequencing method, developed by (Boumen 2005, it is possible to make these decisions such that a time, cost and/or quality optimal test sequence can be constructed. This paper shows with two case studies that test time can be reduced up to 20% without loss of quality with this method. The first case study is related to the test phase during the manufacturing of a lithographic machine. The second case study is related to the reliability testing of a first of a kind lithographic machine.