The CellMask™ Plasma Membrane Stains allow fast and uniform labeling of the plasma membrane without the cell-type differences exhibited by lectins. These stains may be used as a segmentation tool for HCS (high-content screening), as well as to stain cellular plasma membranes for standard fluorescence microscopy. The stain survives fixation, but not permeabilization, so it is not suitable for experiments that also involve probing internal targets via antibodies.