The vascular endothelium has become an increasing focus of research over the last 15 years. Nitric oxide and endothelin appear to have important and opposing actions on vascular tone, smooth muscle proliferation and platelet/monocyte activation, and endothelial dysfunction affecting the L-arginine/nitric oxide and endothelin systems both appear to be crucial to atherogenesis and to the pathophysiology of many forms of cardiovascular disease. Additionally, a number of new drugs of major clinical