The Human Metabolome Database (HMDB) has been significantly expanded and enhanced in its latest release (version 3.0), which was released on September 18, 2012. The database now contains over 40,000 annotated metabolite entries, a 600% increase from the previous version (2.0). This expansion includes both 'detected' metabolites (with measured concentrations or experimental confirmation) and 'expected' metabolites (for which biochemical pathways are known or human intake/exposure is frequent but have not yet been detected in the body). The new release also features increased data on biofluid or tissue concentration, reference spectra, and data fields per entry. Additionally, new visualization tools and data content have been added, including improved spectral viewing, more powerful chemical substructure searches, an enhanced chemical taxonomy, and interactive pathway maps. These enhancements aim to make HMDB more useful for metabolomics and clinical researchers, providing a comprehensive resource for studying the human metabolome.The Human Metabolome Database (HMDB) has been significantly expanded and enhanced in its latest release (version 3.0), which was released on September 18, 2012. The database now contains over 40,000 annotated metabolite entries, a 600% increase from the previous version (2.0). This expansion includes both 'detected' metabolites (with measured concentrations or experimental confirmation) and 'expected' metabolites (for which biochemical pathways are known or human intake/exposure is frequent but have not yet been detected in the body). The new release also features increased data on biofluid or tissue concentration, reference spectra, and data fields per entry. Additionally, new visualization tools and data content have been added, including improved spectral viewing, more powerful chemical substructure searches, an enhanced chemical taxonomy, and interactive pathway maps. These enhancements aim to make HMDB more useful for metabolomics and clinical researchers, providing a comprehensive resource for studying the human metabolome.