A method has been developed to examine the relationships between titanium implants in bone and the immune and hemopoietic cell populations in the adjacent bone marrow; it involves the use of miniaturized implants in the diaphysis of mouse femurs. After surgical placement of the implants, mice were sacrificed and the femurs were either embedded directly in Epon for preparation of ground sections or were decalcified in EDTA, embedded in Epon, subjected to a fracture technique to remove the implant, and sectioned for light and electron microscopy. Scanning electron microscopy revealed that the surfaces of implants removed in this way were virtually free of tissue remnants. Ground sections showed bone in direct contact with the implant surface, providing the first evidence of osseointegration in mice. In addition, an extensive surface of the implant interfaced directly with regenerated bone marrow, a condition that persisted for at least 18 weeks. Some bone marrow cells forming an incomplete layer in contact with the titanium interface had morphologic characteristics of macrophages and giant multinucleated cells. The results demonstrate a long-term integration between titanium implants and cellular elements of bone marow and provide an experimental model to examine the possible implications of this interaction on the processes of Iymphopoiesis and hemopoiesis. Keywords: bone marrow, giant cells, hemopoietic microenvironment, mice, titanium implant