Metal enhanced DAB technology permits detection of extremely low concetrations of tissue antigens. This kit provides a sensitive means for detecting peroxidase labeled antibodies and conjugates. HistoMark Black contains cobalt-enhanced DAB that produces a black, cobalt- DAB polymer with a signal 5-10 times more sensitive than DAB alone. The kit contains the nuclear counterstain, Contrast GREEN, a solution of methyl green that contrasts sharply with black. Blocking solution is provided to prevent endogenous peroxidase activity. The precipitates from HistoMark Black are alcohol and xylene insoluble, allowing section to be mounted in aqueous or xylene-based mounting media.