n-Prop]yl gallate (0.1 to 0.25 molar, in glycerol) reduces by a factor of 10 the rate of fading of fluorescence of cell structures labeled with tetramethylrhodamine or fluorescein-conjugated antibodies. Hence, prolonged photographic exposure of immunofluorescently labeled cells in the fluorescence microscope yields images with increased sensitivity, making feasible multiple data collection, as with serial optical sectioning.