In recent years there has been rapid progress in research on vascular endothelium. This has led to significant advances in our understanding of the structure and function of vascular endothelium in health and disease, including such aspects as the permeability of endothelium in relation to its ultrastructural correlates, theoretical basis, regulatory factors, and role in atherogenesis; the interaction between endothelium and blood cells; the endothelial release and processing of a number of important physiological agents, such as eicosaids, hemostatic factors, and histamine; the cell biology of endothelium with respect to the cytoskeletal apparatus, cell activation, and cell locomotion; and the role of endothelium in microcirculatory regulation in rmal and pathophysiological circumstances. A Symposium on Vascular Endothelium in Health and Disease was held on August 5-6, 1987, at the Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan, Republic of China, following the 4th World Congress for Microcirculation in Japan. Experts working on various aspects of vascular endothelium came from allover the world to participate in this two-day Symposium and gave excellent presentations. This volume, embodying the proceedings of that Symposium, is a collection of the papers given by the speakers with, in many cases, further updating and new information added subsequent to the Symposium. The Institute of Biomedical Sciences (IBMS), the site of this Symposium, is a newlJl established research institution, which has vascular endothelium as one of its areas of research emphasis.