Most of the results on the effects of sympatholytic agents on vascular remodelling came from studies involving hypertensive animals. Therefore, it is often difficult to dissociate the antihypertensive property of the drugs from those caused by the direct action of the drugs on the structure of the blood vessels. However, some general conclusions can be drawn in some areas. Very little information is available on the effects of sympatholytic agents on the structure and function of the endothelial cells, and on the structure of the internal elastic lamina. Necrotic changes of the endothelial cells, and destruction of the internal elastic lamina present in hypertensive animals are prevented with sympatholytic agents, which may be related to the antihypertensive property of the drugs. The density of the fenestrations in the internal elastic lamina is decreased by sympathectomy. In the media, proliferation of vascular smooth muscle cells in growing animals is usually interfered with by sympatholytic drugs, so that the medial mass is normally smaller than that in the untreated control. In most animals, treatment of the animals with sympatholytic agents causes an increase in the biosynthesis, or accumulation of collagen in several types of arteries in the rats and rabbits. In addition to adrenergic nerves, the density of some peptidergic nerves is also reduced by these drugs. The effect of sympathectomy on lumen size is less clear, because lumen size was increased in some studies, and decreased in others. It is clear that remodelling of the vessel wall does occur in some instances, but in general, it is important to distinguish the growth retardation of the animals due to the treatment, from the effect which might be specific to the vessel wall.