HiLyte™ Fluor 750 acid, SE is the longest-wavelength amine-reactive HiLyte™ Fluor dye currently available. Its fluorescence emission maximum at 778 nm is well separated from commonly used far-red fluorophores such as HiLyte™ Fluor 647 or allophycocyanin (APC), facilitating multicolor analysis. With a peak excitation at ~754 nm, conjugates of HiLyte™ Fluor 750 dyes are well excited by a xenon-arc lamp or dye-pumped lasers operating in the 720–750 nm range. The HiLyte™ Fluor 750-protein conjugates are suitable for immunofluorescent staining, in situ hybridization, flow cytometry and other biological applications. The kit has all essential components for performing the conjugation reaction and for purifying the HiLyte™ Fluor 750-protein conjugates. The kit is able to perform three conjugation reactions with each reaction labeling up to 200 µg IgG.