Chromogenic and luminometric substances are also available for horseradish peroxidase (HRP). The "classic" chromogen used with HRP is diaminobenzidine (DAB). In the presence of H₂O₂, HRP will oxidize DAB, creating a water insoluble brown precipitate. DAB has two primary disadvantages, it is relatively insensitive and it is a potential carcinogen which must be decontaminated before disposal.

The sensitivity and convenience of HRP-based detection has been greatly enhanced by the use of luminol as a chemiluminescent substrate. HRP catalyzes the reduction of H₂O₂ to H₂O and then recovers the electrons used for this reduction from luminol, generating an oxidized luminol radical. The luminol radical reacts with O₂ to create O₂^-. The superoxide anion then reacts with a second luminol radical to produce a luminol endoperoxide, which subsequently decays with emission of light. The chemiluminescent reaction of HRP with luminol can be enhanced up to 104 fold by the inclusion of a variety of compounds, including substituted phenols, amines and napthalene derivatives. The mechanism of enhancement is still unclear, but it is theorized that the enhancers act as "electron conduits," channeling electrons more rapidly along the series of reactions from HRP + luminol to light emission.

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