Abstract
This commentary briefly reviews the background for the development of the horseradish peroxidase-diaminobenzidine tetrahydrochloride histochemical method originally described by Graham and Karnovsky in their citation classic, reprinted in full in this issue of Journal of Histochemistry & Cytochemistry. Some of the method's subsequent applications, including its use as a macromolecular tracer for kidney glomerular permeability and use in immunoelectron microscopy and other immunoassays, are also discussed.