The E. coli Metabolome Database (ECMDB) is a comprehensive, high-quality, freely accessible, online database of small molecule metabolites found in or produced by Escherichia coli (E. coli strain K12, MG1655). Escherichia coli is perhaps the best studied bacterium on earth and has served as the "model microbe" in microbiology research for more than 60 years. The ECMDB is essentially an E. coli "omics" encyclopedia containing detailed data on E. coli's genome, proteome and its metabolome. ECMDB is part of a suite of organism-specific metabolomics databases that includes DrugBank, HMDB, YMDB and SMPDB. As a metabolomics resource, the ECMDB is designed to facilitate research in the area gut/microbiome metabolomics and environmental metabolomics. The ECMDB contains two kinds of data: 1) chemical data and 2) molecular biology and/or biochemical data. The chemical data includes more than 2700 metabolite structures with detailed metabolite descriptions along with nearly 5000 NMR, GC-MS and LC-MS spectra corresponding to these metabolites. The biochemical data includes nearly 1600 protein (and DNA) sequences and more than 3100 biochemical reactions that are linked to these metabolite entries. Each metabolite entry in the ECMDB contains more than 80 data fields with approximately 65% of the information being devoted to chemical data and the other 35% of the information devoted to enzymatic or biochemical data. Many data fields are hyperlinked to other databases (KEGG, PubChem, MetaCyc, ChEBI, PDB, UniProt, and GenBank). The ECMDB also has a variety of structure and pathway viewing applets. The ECMDB database offers a number of text, sequence, spectral, chemical structure and relational query searches. These are described in more detail below. Accessing the database The ECMDB's content may be explored or searched using a variety of database-specific tools. The text search box (located at the top of every ECMDB page) allows users to conduct a general text search of the database's textual data, including names, synonyms, numbers and identifiers. The ECMDB employs a software tool called "Elastic Search" that allows misspellings and fuzzy text matching. Using the text search, users may select either metabolites or proteins in the "search for" field using the pull-down box located on the right side of the text search box. In this way it is possible to restrict the search to only return results for those items associated with E. coli metabolites or with E. coli proteins. The ECMB has 7 selectable tabs located at the top of every page including: 1)