New genetic technologies, combined with a well-characterized genome, make the mouse the preferred mammalian model for human disease. The generation and characterization of mouse strains harboring genetically predetermined pathobiological syndromes is critical to biomedical research. The Jackson Laboratory is the leading center of mouse genetics research and the development of mouse models for human diseases including cancer, diabetes, autoimmune diseases, age-related diseases, blood disorders, and neurodegenerative disorders. To fully develop and exploit the biomedical potential of these models, Jackson researchers must have access to critical cutting-edge technologies that allow comprehensive genetic and phenotypic characterization of these models at the cellular level. Multicolor analytical flow cytometry is an essential characterization tool for phenotyping and identifying low-frequency cell subpopulations. Research at Jackson is currently limited by the 8-color maximum of the FACSVantage DiVa cell sorter and increasing demand on this instrument. It is not practical to upgrade the sorter to accommodate additional colors; furthermore, using the FACSVantage for analytical experiments impedes research projects that require its sorting capabilities. [unreadable] [unreadable] Funding is requested for a state-of-the-art Becton-Dickinson LSR II analytical cytometer with 13-color capability, which will increase the specificity, scope, and accuracy of phenotyping and population identification experiments while reducing the amount of sample needed, thereby decreasing the number of mice required for analyses. The BD-LSR-II achieves improved data resolution and reproducibility, as well as reduced experiment times and cost. Unlike the sorter, researchers with minimal technical training can independently operate the BD-LSR-II, freeing the FACSVantage and the technician from analytical experiments and maximize both sorting and analytical capabilities. Purchase of the BD-LSR-II is a cost-effective way to increase the power and efficiency of the Flow Cytometry Service, address unmet research needs of 11 Jackson investigators with 16 NIH funded grants, and enhance mouse model databases and repositories that benefit the entire biomedical community. [unreadable] [unreadable] [unreadable]