Communication in open heterogeneous multi agent systems is hampered by lack of shared ontologies. To overcome these problems, we propose a layered communication protocol which incorporates techniques for ontology exchange. Using this protocol, the agents gradually build towards a semantically integrated system by establishing minimal and effective shared ontologies. We tested our approach, called anemone, on a number of heterogeneous news agents. We show how these agents successfully exchange information on news articles, despite initial difficulties raised by heterogeneous ontologies. Categories and Subject Descriptors I.2.11 [Artificial Intelligence]: Distributed Artificial Intelligence--multiagent systems, coherence and coordination; D.2.12 [Software Engineering]: Interoperability--data mapping General Terms Languages, Theory Keywords Ontology negotiation, Semantic interoperability, Ontology alignment