Oxidation catalyzed by H+ ions improves the silver intensification of 3,3'-diaminobenzidine staining by strongly suppressing tissue argyrophilia.

We found that a 15-min treatment of tissue sections with 2 M/l H2O2 dissolved in 6 M/l sulphuric acid strongly suppresses the argyrophilia of tissue elements, thus facilitating selective silver intensification in histochemical procedures. When applied inserted between the 3,3'-diaminobenzidine reaction and physical development, this treatment allows the selective and sensitive visualization of very low levels of peroxidase activity.