This proposal describes a diverse group of PHS-supported research projects that encompass a broad range of contemporary biological applications of quantitative electron microscopy. The projects include: delineation of mechanisms of intracellular transport of glycoprotein hormones of the anterior pituitary; analysis of the subcellular distribution of unique ferromagnetic glycoconjugates with concomitant ultrastructural localization and biochemical characterization of specific organelles and membrane domains in receptor-mediated endocytosis; characterization of the distribution of DNA excision repair in the genome of human cells damaged with ultraviolet radiation or chemical carcinogens; morphometric analysis of the pathogenesis of the structural and functional derangements of sympathetic neurons in streptozotocin-induced diabetic autonomic neuropathy and acrylamide-induced axonopathy; quantitative ultrastructural autoradiographic characterization of arrhythmogenic lipid metabolites in ischemic myocardium; analysis of mechanisms of regulation of myocardial adrenergic responsiveness with ultrastructural identification of cell surface and internal loci of beta-receptors; morphometric analysis of cardiac myocyte gap junctions in electrophysiologically normal and abnormal myocardium; development of new algorithms for quantitative analysis of electron microscopic autoradiographs and computer-assisted image segmentation and structure identification. Current research activities rely primarily on a 25 year old Philips EM-200 for which availability of replacement parts is no longer guaranteed by the manufacturer. Access to other research electron microscopes is severely limited. Acquisition of a state of-the-art transmission electron microscope will substantially reduce the need for photography and laborious manual analysis of images thus facilitating development of new research applications and promoting optimal usage of shared instrumentation.