As Ontologie knowledge gets more and more important in agent-based systems, its handling becomes crucial for successful applications. In the context of agent-based applications, we propose a hybrid approach, in which part of the ontology is handled locally, using a "client component", and the rest of the ontological knowledge is handled by an "ontology agent", which is accessed by the other agents in the system through their client component. In this sort of "caching" scheme, most frequent ontologie queries tend to remain stored locally. We propose specific methods for representing, storing, querying and translating ontologies for effective use in the context of the "JITIK" system, which is a multiagent system for knowledge and information distribution. We report as well a working prototype implementing our proposal, and discuss some performance figures.