The recombinant CFP (Cyan Fluorescent Protein) is expressed and purified from transformed E. coli using a method that ensures high purity and maximal CFP fluorescence. The protein is suitable as a control reagent for CFP expression studies or as a labeling reagent. Applications include: Use as standards for SDS-PAGE, Western blot analysis of CFP transfected cells, label other proteins, calibration of fluorometers and flow cytometers, fluorescence microscope, or microinjection of CFP into cells and tissues, etc.