This protocol describes a method to assess concentrations of free cytoplasmic calcium (Ca2+) in cultured RAW 264.7 cells. This objective is accomplished with the Ca2+-sensitive fluorescent dye, fluo-3, which permeates cells as an ester and is hydrolyzed in the cell to its Ca2+-sensitive acidic form. Fluorescence is measured over time with adherent cells that have been washed free of extracellular dye.