Flow cytometry viability assays are essential tools in cellular biology, focusing on quantifying the proportion of live cells in a sample by utilizing fluorescent dyes that distinguish between live and dead cells based on membrane integrity. Live cells typically exclude dyes like propidium iodide (PI), which intercalates with DNA in dead cells, while dead cells take up these dyes due to compromised membranes. 

These assays are widely applied in cancer research to evaluate the effectiveness of chemotherapeutic agents, in microbiology for rapid quantitative measurements of microbial viability, and in immunology to assess lymphocyte health under various conditions.

Flow cytometry offers advantages over traditional methods, including speed and throughput—analyzing thousands of cells per second—and quantitative precision, providing comprehensive profiling of cell populations beyond mere viability assessment.

Overall, flow cytometry viability assays are indispensable in modern biological research, enabling rapid and reliable assessments of cell health across diverse scientific disciplines and enhancing our understanding of cellular dynamics in health and disease.