There are several red-emitting fluorophores available for immunofluorescence studies, including tetramethylrhodamine, lissamine rhodamine, Texas Red, and cyanine 3.18; however, it is unclear which of these is best. The present study compared the brightness of these fluorophores to that of fluorescein. Staining was attempted using a primary antibody raised against serotonin and a secondary antibody that was conjugated with either fluorescein or one of the red fluorophores. The intensity of staining was determined densitometrically. It was found that a conjugate of cyanine 3.18 provided significantly brighter staining that conjugates of any of the other fluorophores, including fluorescein. It is concluded that cyanine 3.18 should be useful for multicolor fluorescence experiments and that it may be the brightest fluorophore available for single-color fluorescence immunocytochemistry.