The current release of ProTherm, Thermodynamic Database for Proteins and Mutants, contains more than 10 000 numerical data (300% of the first version) of several thermodynamic parameters, experimental methods and conditions, reversibility of folding, details about the surrounding residues in space for all mutants, structural, functional and literature information. In the current version, we have added information about the source of each protein, identification codes for SWISS-PROT and Protein Information Resource and unique Protein Data Bank (PDB) code for proteins with relevant source. We have also provided additional options to search for data based on PDB code, number of states and reversibility. ProTherm is cross-linked with other sequence, structural, functional and literature databases, and the mutant sites and surrounding residues are automatically mapped on the structure. The ProTherm database is freely available at http://www.rtc.riken.go.jp/jouhou/protherm/protherm.html.