Many advanced grid applications need access to ontologies represent-ing knowledge about a certain application domain. To deal with the high heterogeneity of available ontologies, we propose a general ser-vice-oriented middleware for making ontologies accessible to grid ap-plications. Our implementation is integrated in the German D-Grid in-frastructure and provides several applications a uniform access to biomedical ontologies such as Gene Ontology, NCI Thesaurus and several OBO ontologies.