Abstract The effect of chemical sympathectomy with 6-hydroxydopamine (6-OH-DA) on collagen formation in the aortic wall was investigated in rabbits and rats. Eight weeks after 6-OH-DA treatment of rabbits, there was a significant increase an collagen content in aortas and histologic changes in the elastic elements within the media. The possibility of a direct effect of 6-OH-DA on connective tissue formation was investigated in a subsequent experiment in rats. The rates of collagen synthesis and prolyl hydroxylase activity (PHA) were determined in aortas and in the fibrotic granuloma around subcutaneously implanted polyvinylalcohol sponges. Rates of collagen synthesis and PHA were significantly increased in the aortas of 6-OH-DA treated rats, but not in fibrotic granuloma, confirming the changes seen in the aorta of rabbits and suggesting that 6-OH-DA does not directly affect collagen synthesis. We conclude that the sympathetic nervous system influences the metabolic activity of the aorta. Our data indicate that when the aortic wall is deprived of adrenergic nervous stimulation, changes occur which resemble those seen in natural aging of the aorta. It is plausible to assume that such a metabolic derangement in the vessel wall will make these vessels more vulnerable to additional stresses.