The Human Protein Interaction Database (HPID, was designed 1) to provide human protein interaction information pre-computed by a statistical method from existing structural and experimental data, 2) to provide integrated human protein interactions derived from BIND, DIP and HPRD, and 3) to find proteins from the databases that potentially interact with proteins submitted by users. A score composed of three parts is assigned to the predicted interaction data, and those interactions with high scores were found reliable. HPID allows the user to use the protein IDs in EMBL, Ensembl, MIM, RefSeq, HPRD and NCBI to search protein interactions of interest. A set of web-based software tools has also been developed so that users can visualize and analyze protein interaction networks.