This proposal is a revised application for an analytical electron microscope with image analysis capabilities. The instrument requested will replace obsolete equipment that hampers our research capabilities. A new electron microscope is crucial for the completion of several research projects funded by grants from the National Institute of Health. Acquisition of this equipment will facilitate the work of the investigators. The instrument will be used in several disciplines. Some of the projects using ultrastructural techniques are: (1) the analysis of synapse formation in the brain of developing mammals and the hormonal correlates of this process, (2) the analysis of the distribution of peptide hormones in the anterior pituitary gland and thymus, (3) the analysis and quantification of the process of cardiac necrosis due to catecholamine release and the effects of thiazides in this condition, (4) the analysis of the microvasculature of the brain of the developing dog as a model of intraventricular hemorrhage in the premature human infant. A number of other projects are described in our proposal. The instrument's capabilities for image analysis is as important as the microscope itself: we have no availability of automatic image analysis in our institution or in the immediate area. Some of our investigators have made very complicated arrangements with several colleagues in Europe to conduct their image analysis through collaborative efforts with them: these arrangements arose from necessity and are costly and cumbersome. The instrument will be made available to investigators in our institution through a users committee. At present, the electron microscope facilities at this institution are antiquated and over-burdened by too many users. A research quality electron microscope with image analysis capabilities will ease the access problem, improve the quality of our ultrastructural analysis, improve our productivity, and extend our research into techniques not presently available in our facilities.