We have developed the database, "ProTherm:Thermodynamic Database for Proteins and Mutants," which contains more than 11,000 numerical data for several important thermodynamic properties, structural information of proteins and mutants, experimental methods and conditions, and, functional and literature information. ProTherm can be searched through WWW on various conditions with different options for output. In addition, it is cross-linked with structure, function and literature databases such as PDB, PMD, ENZYME, SWISS-PROT, PIR and PubMed. The structure of mutation sites and surrounding residues can be directly viewed through 3DinSight, which is developed in our laboratory. ProTherm is freely available at above URL.