Fluorescence activated cell sorting and analysis are widely used in clinical and biological studies to analyze and sort cells or other particles at rates of several thousand per second on the basis of fluorescence, light scattering or other optical properties. The prototypes of most instruments now used for these purposes as well as many biological and clinical applications of these instruments were developed under this grant. We now plan to investigate the use of ultrasound as a novel means of cell analysis in flow. If this proves feasible, we will incorporate acoustic detection in a sorter and correlate ultrasound measurements on different types of cells with the other measurement parameters available in flow cytometry. For our FACS instruments, we also plan to increase rates of sorting and analysis, improve efficiency of discriminating and sorting very rare cells, extend the range of optical scatter and infrared measurements, and develop better means of data management, analysis and display using a super-mini computer (VAX 11/780) interfaced with the FACS. Biological and clinical applications projects serving as interactive test systems for these developments include identifying small functional subsets of lymphoid cells, selecting hybridoma switch variants producing new types of immunoglobulins, cloning lymphocyte differentiation antigen genes (e.g. Leu-1 and Leu-2) via DNA transformation, and monitoring passage of Rh+ red cells from fetus to mother during pregnancy.