o-Dianisidine dihydrochloride is primarily used as a reagent in chemical laboratories for the detection and quantification of various substances. It is commonly employed in the synthesis of dyes, particularly azo dyes, which are widely used in the textile industry for coloring fabrics. Additionally, it serves as an intermediate in the production of pigments and other colorants. In analytical chemistry, it is utilized as a chromogenic agent in spectrophotometric assays to measure the concentration of specific compounds, such as peroxidase enzymes. Its ability to form colored complexes makes it valuable in biochemical and clinical research for identifying and studying enzymatic activities. However, due to its potential carcinogenicity, handling requires strict safety precautions and controlled environments.