A thin continuous layer of cells covers the inside of all our blood vessels, separating blood from our tissues and cells. Unlike other cells in the body, blood does not clot when in contact with healthy endothelial cells. This unique and vital property stems from the secretion of molecules that prevent blood coagulation, and that rapidly dissolve blood clots if they do form. The endothelium is not however a one-trick-pony; in addition to controlling blood coagulation, they play essential roles in regulating blood flow, tissue repair and growth, and inflammation within the vasculature and adjacent tissues. Endothelial cells control all of these different processes through the secretion of a large number of different molecules. In effect, the vascular endothelium functions as a highly specialised multi-tasking secretory machine that responds rapidly to changes in its local environment. Alterations to the normal secretory function of endothelial cells are though to contribute to an increased risk of hypertension and atherosclerosis; major causes of stroke and heart attacks. Our research is aimed at trying to understanding the cellular mechanisms that regulate secretion from these cells. We focus particularly on the secretion of peptides and proteins involved in the control of blood coagulation (von Willebrand factor and tissue plasminogen activator) and inflammation (p-selectin and small cytokines such as interleukin-8). We combine biochemical, molecular, cell biological and biophysical approaches to directly analyse the synthesis, storage and secretion of these molecules in single endothelial cells. Understanding how the secretory function of endothelial cells is controlled under normal conditions will shed light on the changes that occur during disease and help us to develop new strategies for the treatment of vascular disorders