Fluorescein isothiocyanate (FITC) is a derivative of fluorescein used in wide-ranging application including labeling reagents. FITC has excitation and emission spectrum peak wavelengths of approximately 495 nm/519 nm, giving it a green color. FITC-protein conjugates are suitable for immunofluorescent staining, in situ hybridization, flow cytometry and other biological applications. The kit has all the essential components for performing the conjugation reaction and for purifying the FITC-protein conjugates.