Manual ontology building in the biomedical domain is a work-intensive task requiring the participation of both domain and knowledge representation experts. The representation of biomedical knowledge has been found of great use for biomedical text mining and integration of biomedical data. In this chapter we present an unsupervised method for learning arbitrary semantic relations between ontological concepts in the molecular biology domain. The method uses the GENIA corpus and ontology to learn relations between annotated named-entities by means of several standard natural language processing techniques. An in-depth analysis of the output evaluates the accuracy of the model and its potentials for text mining and ontology building applications. The proposed learning method does not require domain-specific optimization or tuning and can be straightforwardly applied to arbitrary domains, provided the basic processing components exist.