Calcein AM is a cell-permeant dye that can be used to determine cell viability in most eukaryotic cells. In live cells the nonfluorescent calcein AM is converted to a green-fluorescent calcein, after acetoxymethyl ester hydrolysis by intracellular esterases. This dye is also available in our special packaging (C-3100) and as 1 mg of the solid (C-1430). For a longer wavelength version of this dye, check out our new CellTrace calcein red-orange AM (Cat. no. C-34851).