The Andromeda X His-Tag Labeling Kit provides convenient means for the site-specific, purification-free labeling of His-tagged proteins with our fluorescent RED-tris-NTA 2nd Generation dye. This kit can be used for the labeling of any protein carrying a polyhistidine-tag (His-Tag) and contains material sufficient for up to 5,000 single-point Andromeda measurements. Labeling can be completed in 30 min, no removal of excess dye is required. The RED-tris-NTA 2nd Generation dye can bind efficiently to His-tags which contain at least six histidines with a Kd in the single digit nM range. By following this protocol, optimized for nearly 100 % binding of dye to His-tagged proteins eliminates an additional purification step and ensures the best results.