We are proposing to add a 4-laser LSRII cell analyzer that will measure two light scatter signals and up to 18 fluorescence signals to the instrumentation in the Stanford Shared FACS Facility. The system will include somewhat higher power lasers than standard versions of the FACSAria in order to obtain the best possible data quality and promote maximal use of varied multicolor reagent combinations. The Facility has a long history of developing and supporting advanced instrumentation and collaborating in reagent development for flow cytometry. Bringing this instrument into the Stanford Shared FACS Facility will advance specific projects that take advantage of its advanced capabilities, catalyze development of new probes and new and expanded combinations of fluorescent cell labels and serve cell sorter users of the Facility by increasing flexibility in allocating work to instruments. A 2-laser sorter in the Facility has limited capabilities and is becoming unmaintainable, and one 3-laser sorter was assembled in our instrument development program and is not properly maintainable in a routine service environment. The FACSAria II will immediately replace the 2-laser instrument and will assure that the cell sorting needs of the Facility's users can be met even if the 3-laser sorter must be shut down before it can be properly replaced. This FACSAria II will provide a number of capabilities that are not now available on the Facility's existing 2- and 3-laser systems, particularly a 532nm laser, an expanded array of detectors for the 405nm laser and routine BSL-2 sorting capability. The existing instruments in the Stanford Shared FACS Facility are used to reasonable capacity, so it will be good to introduce an instrument that does the most to expand effective capacity and offers new capabilities not present among the existing instruments. The system is based on the now well-established FACSAria platform. Lasers in a range of wavelengths are likely to become less expensive while offering higher powers in the next few years. If development of new reagents and dye proceeds well, instruments with similar capabilities could become commonplace in the not too distant future. Almost all the work done in the Stanford Shared FACS Facility is health related research ranging from basic studies in molecular biology, genetics and development to AIDS-related clinical research. The large majority of the work in the Facility is NIH supported. Public Health Relevance: Flow cytometry (FACS) is one of the most powerful and widely used tools in cellular and molecular biology research. The 125 faculty investigators who used the Stanford Shared FACS Facility in 2007 include leaders in many areas of biomedical research employing FACS technology. A high capability 4-laser FACSAria II in this environment will facilitate the development of new methods and contribute to new research results that will be disseminated among the research community. Research using this instrument will lead to discoveries in both basic and clinical areas that would be more difficult or impossible without it.