Although FITC is still the most popular fluorescent labeling dye for preparing green fluorescent bioconjugates, there are certain limitations with FITC, such as severe photobleaching for microscope imaging and pH-sensitive fluorescence. Protein conjugates prepared with FITC-xtra are far superior compared to the corresponding FITC conjugates. FITC-xtra conjugates are significantly brighter than FITC conjugates and are much more photostable. Additionally, the fluorescence of FITC-xtra is not affected by pH (4-10). This pH insensitivity is a major improvement over FITC, which emits its maximum fluorescence only at pH above 9. FITC-xtra has spectral properties almost identical FITC. In addition, FITC-xtra give much higher conjugation yield under mild conjugation conditions than FITC. Like 5-FITC, FITC-xtra antibody conjugates have excitation ideally suited to the 488 nm laser line, making them alternatives to the corresponding FITC-labeled antibody conjugates. Under the same conditions tested, FITC-xtra antibody conjugates give much higher signal/background ratios than the corresponding FITC-labeled conjugates.