BrdU staining system uses a biotinylated monoclonal anti-BrdU, thus eliminating the need for a species-specific secondary antibody. As a result, BrdU staining can be performed in rabbits, rats and mice without problems of crossreactivity or spurious staining due to the detection of endogenous Ig. Streptavidin-peroxidase with DAB is used for signal generation. Nuclei that have incorporated BrdU will stain dark brown.