The Mouse Genome Database (MGD) is a comprehensive community database that integrates genetic, genomic and phenotypic information about the laboratory mouse. MGD provides detailed information about genes and genetic markers, elemental data from mapping experiments, descriptions of molecular segments including ESTs, probes, and cDNA clones, homology information between mouse and many other mammalian genomes, and phenotypic descriptions of gene mutations, gene function and mouse strains. All data are supported by citations. Interactive graphical displays of cytogenetic, genetic and physical maps are available. User support is provided through dedicated staff, bulletin boards, and user documentation. MGD can be accessed at http://www.informatics.jax.org