Human, rabbit and canine articular cartilage was prepared for SEM by fixation in isosmolal glutaraldehyde and freeze-fracture following dehydration. These techniques produced clear images of the bone, marrow and vessels in the subchondral region. Generally, cavities larger than 40 microns contained elements typical of marrow. Capillaries ran through the bone in cylindrical channels 20-40 microns wide. These channels were surrounded by concentric lamellae of bone and were in all respects Haversian canals within osteons. A minority of these channels opened into the calcified articular cartilage and there were preceded by cells which appeared to be cutting into the cartilage. Most vascular channels, however, were separated from the cartilage by a layer of bone. We conclude that the vessels within subchondral bone are present primarily to supply the bone through a network of mature osteons.