The conjugated goat anti-mouse and anti-rabbit polymer-horseradish peroxidase secondary antibody reacts with heavy and light chains on mouse and rabbit IgG. It reacts with all mouse and rabbit IgG subclasses and with mouse and rabbit IgM. The new and innovative HRP-polymerization technology provides a significant increase in staining sensitivity when compared to other conventional HRP-conjugated secondary antibodies. Avidin-biotin blocking procedures are not necessary when using the MACH 2 conjugated secondary antibodies. The overall staining procedure uses one less reagent (streptavidin peroxidase) and rinsing step, eliminates avidin-biotin blocking procedures, and may reduce overall staining time. It can be used manually and on automated stainers.