Flow cytometry and cell sorting have become established technologies in cell biology. A large number of methods for staining and measuring properties of individual cells are available. New protein and DNA dyes have made it possible to analyze large number of cells individually for multiple properties. These techniques have had a large impact on cellular immunology and the study of cell proliferation. New fluorescent molecules that report on intracellular conditions are used increasingly to study cell physiology. Chromosome analysis and sorting by flow cytometry is becoming a valuable tool and refinements in the techniques for manipulating small quantities of DNA will increase the application of chromosome sorting in molecular biology. The analysis of rare cell populations is still hampered by shortcomings in the present generation of commercial instruments. Rare even analysis will be improved when high-resolution, high-speed sorters are available. Future technology will make use of non-linear effects in fluorescence induction. An improved understanding of non-linear phenomena will lead to new techniques for single-cell analysis.