This protocol describes a method to assess concentrations of free cytoplasmic calcium, [Ca2+]i, in cultured adherent RAW 264.7 cells, using a 96-well plate format. This objective is accomplished by using the Ca2+-sensitive fluorescent dye, fluo-3, which permeates cell membranes as an ester and is
hydrolyzed in the cell to its Ca2+-sensitive acidic form.