The trypan blue assay is a method using cell impermeable dye, trypan blue, for determining cell viability. Trypan blue is excluded from the live cells who possess intact cell membranes, whereas in dead cells with compromised membrane integrity, trypan blue can readily penetrate and stain the cytoplasm blue. Upon analysis by light microscope, the number of stained cells can be examined against the total cell population. The number of stained cells will represent the percentage of dead cells in the entire population.