The newly deposited bone which was laid down on necrotic bone in the experimentally produced osteochondral chips in the knee joint of 16 sheep and rabbits remained unmineralized and undermineralized in which respect it resembled osteomalatic bone. Local factors which interfere with the mineralisation of a new covering bone should be considered in the pathogenesis of osteomalacia, in healing of aseptic bone necrosis and fractures, and incorporation and fate of bone transplants.