AbstractThe presence of proteoglycans (PGs) was studied in compact lamellar rat and human bone at the electron microscopic level. With the cationic dye cuprolinic blue (CBI), PGs could be demonstrated in the mineralized bone matrix. The amounts of PGs appeared to be equal in the different lamellae and osteons. More CBI‐positive material was found in the outermost lamella of the cortex, in the perilacunar matrix around the osteocyte lacunae, and around the canaliculi. Enzyme digestion with chondroitinase ABC demonstrated that the CBI‐positive rods consisted of PGs. These observations amplify biochemical studies in which PGs have been isolated from the mineralized bone matrix. The presence of CBl‐positive rods in the mineralized matrix suggest that PGs do not have to be removed completely to make the matrix calcif