The HPSF (Human Proteome Structure and Function) database is a repository of structure and function annotations on the 'missing proteins' of the human proteome. The missing proteins that have not been validated at protein level are first extracted from the neXtProt database. The structure folding simulations are then generated by I-TASSER with all homologous templates excluded from the threading libraries. Finally, the functional insights of each protein, including enzyme commission, gene ontology, ligand-binding and subcellular location, are provided by the structure-based function annotation tool, COFACTOR. One goal of the HPSF database is to construct a comprehensive repository consisting of annotations on the folding and function of all missing proteins in human proteome using the cutting-edge bioinformatics methods, which should provide important help to recognize possible protein-coding genes from the 'missing proteins' and to guide further protein characterization experiments. (>>more about HPSF database).