An environmental health science thesaurus is needed to facilitate Semantic Web operations and aid with problem solving in this important cross-domain area. This paper demonstrates the need for an environmental health science thesaurus and reviews metadata generation research that highlights the importance of subject metadata. A conceptual design for building a cross-disciplinary metathesaurus using shared ontologies and other Semantic Web technologies is presented. The design emphasizes a dynamic, distributed approach to thesaurus construction, and builds on Semantic Web developments, especially the integration of multiple ontologies. The paper concludes by identifying candidate terminological sources and identifying a major challenge.