The MMRRC is the official mouse repository of the National Institutes of Health (NIH). The MMRRC distributes and cryopreserves scientifically valuable, genetically engineered mouse strains and ES cell lines with potential value for both the genetics and biomedical research communities. We are a national network of breeding and distribution facilities plus an information coordinating center serving together as NIH's premier repository of spontaneous and induced mutant mouse and cell lines. The MMRRC is committed to upholding the highest standards of experimental design and quality control to optimize the reproducibility of research studies using mutant mice. The MMRRC is supported by the Office of Research Infrastructure Programs, Office of the Director, National Institutes of Health (NIH). Strains of mice are maintained in a cryopreserved state unless demand warrants that a live colony be established. Live mice are supplied from a production colony, from a colony recovered from cryopreservation, or via micro-injection of a cell line into host blastocysts. A MMRRC facility may offer cryopreserved material for resuscitation at the recipient scientist's institution. Functioning as a single repository resource, the MMRRC is comprised of an Informatics, Coordination and Service Center (ICSC) and four regional distribution facilities. They are: The Jackson Laboratory University of California, Davis University of Missouri University of North Carolina, Chapel Hill