This proposal seeks partial support for a Philips CM 12/STEM electron microscope to replace an AEI 801 instrument in the Dental Research Center (DRC) at the University of North Carolina. The DRC was established in 1967 and is one of five NIH funded regional dental research institutes in the nation. Currently, the DRC's electron microscope laboratory houses both SEM and TEM instruments and related technical facilities. The School of Dentistry and its DRC are deeply involved in basic research, with annual grant/contract acquisitions in excess of 4.2 million dollars. In the basic sciences, the DRC operates nationally recognized research programs in mineralized tissue, embryology, teratology, cell biology, collagen biochemistry, hemostasis, neurophysiology, and biomaterials. The School offers graduate research training in oral biology and in eight clinical fields. The AEI 801 was purchased in 1971. Maintained on annual service contract since that time, the instrument can produce reasonable images to 40-60,000X magnification. However, by present standards our AEI is sharply limited as a research instrument which in turn has severely hampered the DRC's current research programs. First, by constantly pressing against the AEI's magnification limit, investigator manuscripts are being returned by editors demanding superior micrographs. Second, our AEI lacks the microprocessor controlled analytical capabilities that are now considered standard for advanced level work, including X-ray microanalysis, electron diffraction, and image processing. Third, our AEI is difficult and expensive to maintain and common problems (alignment drift, vacuum, electrical), together with instrument limitations, actively discourage its use. Fourth, availability and access to other EM facilities on the UNC campus are limited and expensive, primarily because of intensive use these instruments already receive. To move forward by overcoming the four problems identified, the Philips CM 12/STEM is proposed as an instrument with superior resolution, clean ultrahigh vacuum, full analytical capabilities, and microprocessor controlled imaging and operating mode features.