Alexa Fluor® 647 conjugates are the best choice of far red-emitting dyes for multiple-labeling detection with a confocal microscope.A significant advantage of using Alexa Fluor® 647 over lower wavelength-emitting dyes is the low autofluorescence of biological specimens in this region of the spectrum. However, because of its peak emission at 667 nm, Alexa Fluor® 647 cannot be seen well by eye, and it cannot be excited optimally with a mercury lamp. Therefore, Alexa Fluor® 647 is not recommended for use with conventional epifluorescent microscopes. It is most commonly visualized with a confocal microscope equipped with an appropriate laser for excitation and a far-red detector. Alexa Fluor® 647 conjugates are less expensive alternatives to allophycocyanin conjugates for flow cytometry.