Soluble in distilled water. Soluble in 0,1 M potassium phosphate buffer, pH 6,0 (monobasic potassium phosphate adjusted to pH 6,0 with 1,0 M potassium hydroxide) (10 mg/ml yields a clear, red-brown solution). Solutions of HRP can be kept refrigerated for up to a year while maintaining practically undiminished activity. Optimal pH is 6,0 to 6,5 (activity at pH 7,5 is 84% of the maximum). The enzyme is most stable in the pH range of 5,0 to 9,0 (Lit.).

That amount of enzyme causing the production of one mg of purpurogallin in 20 seconds at 20 °C.

Activity is observed with H₂O₂, MeOOH and EtOOH.

Horseradish peroxidase (HRP) is used in biochemistry applications such as western blots, ELISA and Immunohistochemistry. Horseradish peroxidase is used to amplify a weak signal and increase detectability of a target molecule, such as a protein. It is an essentially salt free lyophilized powder. It is commonly used to determine amounts of glucose and peroxides in solution. It has been used in an aspergillus fumigatus rapid susceptibility assay. HRP can be conjugated to antibodies by several different methods including glutaraldehyde, periodate oxidation, through disulphide bonds, and also via amino and thiol directed cross-linkers. HRP is the most desired label for antibodies, since it is the smallest and most stable of the three most popular enzyme labels (HRP, β-galactosidase, and alkaline phosphatase) and its glycosylation leads to lower non-specific binding. A review of glutaraldehyde and periodate conjugation methods has been published. HRP labeled immunoglobulins are used as probes for the demonstration of tissue antigens and in enzyme immunoassay (EIA) systems for determination of soluble and insoluble antigens. It is also useful for tracing neural connections. These include motor and sensory innervation of peripheral organs, and connections of peripheral nerves, ganglia and individual dorsal roots.