CellTrace calcein red-orange AM is a cell-permeant dye that can be used to determine cell viability in most eukaryotic cells. Unlike calcein AM (C-1430, C-3099, C-3100), CellTrace calcein red-orange AM is intrinsically fluorescent; thus, an additional wash step may be necessary to minimize background fluorescence from dye that is not taken up by cells. However, CellTrace calcein red-orange (excitation/emission maxima 577/590 nm) is well-retained by live cells that possess intact plasma membranes, and consequently it is a useful cell tracer and indicator of cell viability.