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.