An alkaline phosphatase (AP) catalyzed metallographic detection of IHC will be presented. Several reducing agents were protected as redox-inactive phosphates and incubated with tissue containing AP-antibody conjugate bound at the desired antigen epitope. The AP catalyzed the hydrolysis of the phosphate to give unmasked reducing agent, which in the presence of silver (I) ion produced nanoparticles of metallic silver (0). Subsequent signal amplification by development of the deposited silver “seeds” produced a signal at the target site that was discernible by bright field microscopy. The development of phosphate-protected reducing agents and the enzyme-catalyzed metallographic detection of some tissue antigens will be presented.