The Human Mitochondrial Protein Database (HMPDb) conveniently consolidates information from a number of other databases, including GenBank, Online Mendelian Inheritance in Man, and the Human Mitochondrial Genome Database. HMPDb "is intended as a tool not only to aid in studying the mitochondrion but in studying the associated diseases" as well. Features include a general database search, a graphical tool for visualizing the mitochondrial DNA sequences, and 3D structures for mitochondrial proteins. Users are welcome to contact the National Institute of Standards and Technology with corrections or other information relating to the database.