An expert system for medical decision making in hepatology has been developed with the aim of assisting medical education. The knowledge representation is based on different slots respectively concerned with structural and protypical description, and system control. Reasoning is performed at two levels considering in sequence syndromes and diseases. Explanations are available at any time during the reasoning process. Educational facilities are provided by using the help sections of the system, which include definitions and descriptions of finding in both health and disease, as well as summaries defining essential clinical and pathophysiological features of all diagnostic hypotheses. The system provides the following educational functions: support to medical decision making, differential diagnosis, knowledge-base consultation, system description and clinical simulation. A good correspondence was found between the conclusions and suggestions provided by the system and those of the attending physicians. The program, which was written in PROLOG and developed under MS-DOS Operating System, runs on IBM-compatible personal computers equipped with hard-disk and mouse.