The National Center for Biomedical Ontology (NCBO) is one of seven National Centers for Biomedical Computing in the United States supported by the National Institutes of Health. As workers in biomedicine recognize the importance of creating structured representations of the entities and the relationships among entities in experimental domains, the NCBO is developing the semantic technologies to use those representations to drive in a wide range of applications in data annotation, data integration, information retrieval, natural-language processing, and decision support. The NCBO is creating Web-based software to facilitate the archiving, peer review, and application of ontologies by workers in biomedicine. In recent years, the use of NCBO resources has been growing exponentially. Currently, more than 65,000 visitors browse the BioPortal ontology repository each month, many of whom seem to visit the site nearly every day. Each month, the NCBO handles more than 3 million Web service calls. Learning what all these users are doing with NCBO technology provides an opportunity to track the requirements of the Semantic Web community in health care and the life sciences. The NCBO continues to explore methods to obtain more information about these users and their needs in an attempt to anticipate trends in the work of biomedical scientists who are embracing semantic technology.