In medicine many exceptions occur. In medical practice and in knowledge-based systems too, it is necessary to consider them and to deal with them appropriately. In medical studies and in research, exceptions should be explained.We present a system, called ISOR, that helps to explain cases that do not fit to a theoretical hypothesis. Starting points are situations where neither a well-developed theory nor reliable knowledge nor, at the beginning, a case base is available. So, instead of theoretical knowledge and intelligent experience, just some theoretical hypothesis and a set of measurements are given. In this chapter, we focus on the application of the ISOR system to the hypothesis that a specific exercise program improves the physical condition of dialysis patients. Additionally, for this application a method to restore missing data is presented.