The paper deals with the role of ontologies in e-learning. We report our research on the application of ontologies in intelligent platforms for self-learning and computer-mediated education that are developed at the Faculty of Informatics, Masaryk University, Brno, Czech Republic. The use of ontologies in the organization of knowledge about the area of learning management systems is tackled first. The next part discusses a new direction of our research aiming at automatic generation of e-learning self-tests based on information extracted from ontologies. A very new topic deals with the preliminary experiments on an ontology-based automatic evaluation of student essays.