Biological trace elements are required for numerous biological processes and by all organisms. We describe a database, dbTEU (DataBase of Trace Element Utilization), that features known transporters and user proteins for five trace elements (copper, molybdenum, nickel, cobalt and selenium) and represents sequenced organisms from the three domains of life. The manually curated dbTEU currently includes approximately 16,500 proteins from >700 organisms, and offers interactive trace element, protein, organism and sequence search and browse tools.