This protein labeling kit comprises the orange fluorescent dye CF532 in succinimidyl ester (SE) form and other necessary materials for labeling 3×1 mg antibody. CF532 has an excitation spectrum optimally matching the 532 nm line of the frequency-doubled Nd-Yag laser. Antibody conjugates of the dye are much brighter than those of Alexa Fluor? 532.