The titanium bone growth chamber consists of two titanium disks held together by two screws. At the level of the intersection between the disks, a 1 mm wide canal penetrates the implant. After implantation, in e.g. the rabbit, tibial metaphysis bone and vessels will grow through this canal, the contents of which are collected four weeks after surgery. Microradiography and a computer-based analysis give a numerical representation of the amount of newly formed bone in the canal. When the bone ingrowth into two identical titanium implants, one inserted in the left and the other in the right tibia, was compared, only small and insignificant differences were found in the same animal. However, when one animal was compared to another, greater differences in the bone-forming capacity were found, in spite of the fact that the rabbits were controlled with respect to race, age and sex. The osseous penetration rate into titanium canals was compared to the bone ingrowth in equally sized pipes of polymerized acrylic cement which had been inserted in the titanium chamber. In these cases there was significantly less bone formed in the cement pipes compared to the titanium controls. Poor biocompatibility of the cement compared to titanium is suggested to be one factor responsible for the reduced bone formation in the cement environment. This may be one reason for the fibrous tissue capsule generally seen around cemented implants.