The study is part of a project aimed at obtaining an autologous, preformed transplant for reconstruction of a defect ossicular chain. In animal experiments we found that bone could be produced in a titanium mould placed in the tibia of the rabbit and dog. To find out whether this observation was applicable in man, 5 patients with ossicular defects were selected. A titanium mould containing two chambers was placed in the proximal tibial metaphysis for 6 months. When the moulds were extracted bone was found in 7 of the 10 chambers. In 2 of these the bone was stable and suitable for ossiculoplasty. On histological examination the same picture as in the animal experiments was found, an outer layer of cortical bone surrounding a system of spongy bone with marrow and haematopoietic cells. Microradiological examination verified the presence of mineralized bone tissue.