The bone-hydroxylapatite interface has been examined directly in the transmission electron microscope (TEM). The bone-hydroxylapatite interface was characterized by using several electron microscopy techniques, including bright and dark field imaging, electron diffraction, high-resolution imaging, and energy dispersive analysis in the scanning-transmission electron microscope (STEM EDS). Mechanical grinding followed by argon-ion milling produced interface regions of unstained and undecalcified rat bone and hydroxylapatite that were transparent to electrons. Thus the exact location of the interface could be established and the bone at the interface studied. Conventional and high-resolution imaging in the TEM demonstrated direct chemical bonding between bone and hydroxylapatite. The bone at the ceramic surface was the same as normal bone away from the interface.