An animal genome database for comparative mapping was developed on a UNIX workstation. Linkage map, cytogenetic map, reference, PCR primer information and mapping homology between species were included in the database. These data can be retrieved by electronic mail system and World Wide Web (WWW) client through the Internet. In addition, an online linkage analysis system was developed using CRI-MAP 2.4; this system includes the management of linkage data, computing of lod score for each pair of genetic markers and construction of linkage map. We have also developed a gene mapping workbench designated as gRanch. The system displays an integrated gene map and 2 kinds of homology maps between species. The functions for linkage data input and the linkage map analysis are included in the gRanch. Furthermore, Mouse Genome Informatics mirror site in Japan has been opened since August 23, 1996. The users of Mouse Genome Database and Gene Expression Database in Asia are invited to connect with the Japan mirror site.