The term endothelial dysfunction (ED) generally refers to a pathological circumstance in which normal endothelial regulation of vasomotor tone is disturbed. ED has been described in a broad range of cardiovascular and related disease states. In association, deranged endothelial function also has the potential to result in abnormal platelet aggregation and monocyte adhesion. Over the past decade, it has become apparent that reduced availability of nitric oxide is a key mechanism for ED. A range of biochemical disturbances, including depressed L-arginine, have been shown to be associated with ED, and recent evidence indicates this may be genetically determined.