As compared with the aminocoumarin derivatives, the Cascade Blue fluorophore shows less spectral overlap with fluorescein, an important advantage for multicolor applications. In addition, this reactive Cascade Blue derivative has high absorptivity, is highly fluorescent and, unlike most dyes, resists quenching upon protein conjugation. Even at low degrees of labeling, Cascade Blue conjugates are significantly more fluorescent than are those of 7-amino-4-methylcoumarin-3-acetic acid (AMCA), and they remain preferred reagents for multicolor flow cytometry. Although a standard DAPI/Hoechst optical filter set can be used with Cascade Blue conjugates, the fluorescence will be brighter when viewed through optical filters optimized for the spectral properties of the Cascade Blue dye.