An important aim in problem-oriented learning at the medical school of the University of Limburg is that a student should be able to test his knowledge in relevant problem situations. This implies that learning resources such as text books and lecture notes are not sufficient. The curriculum of the school confronts the students as early as possible with real-patient encounters as well as a skills laboratory where they practice medical skills. However, many basic biomedical problems cannot be studied on this basis. Computer simulation programs based on mathematical models can give the opportunity to investigate fundamental concepts underlying complex biological systems. In fact modelling and computer simulations have over the last few years become important tools in the analysis of the normal and abnormal behaviour of such systems. Parameters involved can be easily and reproducibly manipulated to show effects on hemodynamic variables, drug levels or chemical reactions correctly and at once. An advantage of such simulations is that students can investigate problems by themselves without patients or experimental animals. Moreover, students learn to formulate hypotheses and to test them quantitatively. We describe here two of the programs developed and used at our medical school in the field of cardiovascular control.