DyLight 405-conjugated secondary antibodies are excited maximally at about 400 nm and fluoresce with a peak at about 421 nm. They are very bright and photostable, but their optimal use is limited to microscopes or flow cytometers equipped with a 405 nm laser and a 420 nm emission filter. Under these conditions, it is possible to perform effective 4-color imaging with good color separation, good photostability, and high sensitivity.