In order to take full advantage of computer-based decision support in clinical practice, it makes sense to combine systems which support the same subject, but contribute to this task in different ways. At the Technical University of Munich, a Combined Clinical Decision Support System (C-CDSS) of this kind has been designed for gastroenterologists. The main goal of the system is to help the physicians in finding information which is relevant for making the right diagnoses or applying the proper therapy to his patients. To achieve this goal, not only systematic knowledge of the medical domain, but also case-based data is useful for a comparison of the actual case with well-documented similar cases of colleagues. The systematic knowledge comprises state-of-the-art textual information and selected multimedia contents in the sense of a standard textbook. The case-based information includes practice-related information on a pool of anonymized cases from clinical routine and also demonstrations of new techniques. By integrating these information resources into one service via a rule-based retrieval system, a powerful decision support system can be generated.