This protein labeling kit comprises the deep-red fluorescent dye CF594 in succinimidyl ester (SE) form and other necessary materials for labeling 3×1 mg antibody. CF594 is spectrally similar to Alexa Fluor? 594 and Texas Red? dye but yields much brighter protein conjugates due to its high quantum yield and exceptional water solubility. CF594 also has excellent photostability ideal for demanding applications, such as confocal microscopy and single molecule imaging. The dye is particularly useful to combine with our blue fluorescent CF350, green fluorescent CF488A and far red CF633 or CF647 for multi-color imaging.