The CASUS-project, a three year publicly funded effort to improve the quality of continuing medical education in Germany, has one major goal: The development and evaluation of an easy-to-handle author-system for problem-oriented learning in medicine. On the theoretical basis of the cognitive apprenticeship-approach, the concept of a teaching and learning database as a hypermedia system was built. The student should learn to manage authentical problems in the form of authentical clinical cases. The step-by-step learning process is expert-guided by the clinical authors of each case. The creation of various differential diagnoses by the learner is strongly supported in the process. The structure of the program can also be used for case-based examinations. In parallel to the technical development, a case-selection process for medical students students in internal medicine was initiated. About 120 relevant diseases were identified to be represented in the CASUS-case library. Prevalence, transferability of knowledge, treatability, urgence of treatment and preventive aspects were used as selection criteria. The system will be evaluated during the implementation of test cases and will then be available to be used by authors and students on a routine basis in 1997.