We are proposing to add a 4-laser LSRII cell analyzer which 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 LSRII in order to obtain the best possible data quality and promote maximal use of varied multi-color 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 all users of the Facility by diverting analytical use from cell sorters to a more appropriate and user friendly instrument. This LSRII will provide a number of capabilities that are not now available on the Facility's several 3-laser systems, particularly a 532nm laser, an expanded array of detectors for the 405nm laser and a High Throughput Sampler. 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. While the system may seem somewhat exotic at this time, it is based on a well established platform. Lasers in a range of wavelengths are likely to become less expensive while offering higher powers. 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. Flow cytometry is one of the most powerful and widely used tools in cellular and molecular biology research. Investigators using the Stanford Shared FACS Facility include leaders in a number of areas of biomedical research employing FACS technology. A high capability 4-laser LSRII in this environment will facilitate the development of new methods that will be disseminated among the research community and it will lead to discoveries in both basic and clinical areas that would be more difficult or impossible without it. [unreadable] [unreadable] [unreadable]