The computerized fact database for the toxicity data of chemicals was constructed at the National Institute of Hygienic Sciences, Tokyo, Japan (biological database, BL-DB). The BL-DB stores data on mutagenicity, teratogenicity, carcinogenicity, and other toxicological tests of chemicals that appeared in the scientific literature. The BL-DB includes information about chemical identification, test system, results of the assays, and a bibliography. The system consists of five modules: data collection, data maintenance, data search, data downloading, and backup. ADABAS is used as a core database management system. Many kinds of test data are stored with the same formats; therefore, users can retrieve data of different toxicological data by the same manner. A user of the BL-DB can use about 50 kinds of commands to interact with the system, and the majority of fields are defined as search fields, thereby facilitating retrieval of target data through many ways. Currently, there are mainly data for the mutagenicity, especially on the Salmonella/microsome assay and the rodent micronucleus assay. These data can be retrieved and used for structure-activity relationship studies.