The AnaTag™ R-PE Labeling Kit is optimized for use in the conjugation of R-Phycoerythrin (R-PE) to antibodies. R-PE, a fluorescent protein from phycobiliprotein family, has broad absorption bands with peaks at 565 nm (eM =1.96 X 106 M-1cm-1), 498 (eM =1.53 X 106 M-1cm-1), and 539 nm (eM =1.62 X 106 M-1cm-1); it therefore can be excited with versatile excitation sources. Its maximal emission can be detected at 578 nm. The broad excitation spectrum also provides the advantage of multi-color immunofluorescent staining or cell sorting. R-PE and the closely related B-PE are the most intensely fluorescent phycobiliproteins having orange fluorescence. They are significantly brighter and more photostable than conventional organic fluorophores. The AnaTagTM R-PE Labeling Kit contains SH-reactive R-PE. SMCC modified R-PE reacts with the thiol groups of target antibody without the need for additional activation, thus simplifying the conjugation protocol. The amount of R-PE supplied in this kit is sufficient for labeling up to 1 mg of antibody. The kit provides all reagents, purification columns and a detailed step-by-step protocol. Native and SMCC-activated R-PE are also available as separate products.