AbstractRivanolR, a fluorescent ethoxy derivative of acridine, interacts at different pH's with both glycosaminoglycans and proteins. The present study utilizes the specific interaction of RivanolR with acidic substances of the ground substance for histochemical studies of the cartilage matrix. This stain was applied to newborn mouse epiphyseal cartilages which were either unextracted or dissociatively extracted by graded concentrations of guanidinium chloride (GuHCl) from 0.5–3.0 M for four days at 25°C. Routinely prepared sections were then stained (0.1% solution) for two minutes at pH's ranging from 2.2–11.2. Stainability of the interterritorial matrix as well as the inner halo zone and outer corona zone of the lacunar matrix varied with pH. Whereas the interterritorial matrix decreased in stainability with rising pH, the halo and corona persisted in stainability up to pH 10.7. Dissociative extractions using GuHCl revealed the unextractable nature of the inner halo zone as well as the extractable nature of the corona above 1.0 M GuHCl concentration. Anionic sites on polyelectrolytes such as glycosaminoglycans are known to stoichiometrically bind many cationic dyes. The precise localization of stain‐reactive glycosaminoglycans or proteoglycans in the region of the perichondrocytic matrix by RivanolR supports prior observations using other cationic stains. Our data demonstrates that RivanolR enables one to visualize the unique perichondrocytic matrix which may be interpreted to be both chemically and morphologically a “matrix within a matrix”.