Elastin was isolated from the thoracic aorta of humans of different ages, sclerotic and nonsclerotic, and studied qualitatively and quantitatively. Sum of collagen and elastin contents of normal aorta showed progressive increasing with age, except for the groups younger than 20 years old, which showed a fall. But proportion of collagen to elastin concentration remained constant in wide age range in the aorta, though markedly diminished with advancing age in the pulmonary artery.The susceptibility of aortic elastin to elastase was expressed as percent solubilized protein N of total elastin N, incubated with elastase in pH8.7 borate buffer under shaking at 37°C for 14 hours. These results showed progressively diminished values with advancing age, but there was no significant difference in the values between sclerotic area and adjacent normal area of the same aorta.Activating by ultraviolet light, the fluorescent spectrum of the solubilized aortic elastin was drawed, using spectrophotofluorometer. Of three fluorescent substances recognised, one showed age-related increasing tendency after 40 years old, whose activation/fluorescence maxima was at 336/400nm. And the intensity of the fluorescence of aortic elastin was not influenced by sclerotic changes.Elastase solubilized aortic elastin was chromatographed using Sephadex-G-100 column. All the samples of aortic elastin showed two peaks, Fraction A with larger molecular weight, and Fraction B with smaller molecular weight. The ratio of A/A+B showed increasing age trend, except for a case of 75 years old, which showed a fall. Elastin from sclerotic area showed higher A/A+B ratio than adjacent normal area of the same aorta.As carbohydrate components of glycoproteins in the elastin fraction from the aorta, hexoses, hexosamines, methylpentose and sialic acid were analyzed. The proportion of the total sugar in elastin fraction showed age related increasig tendency. Of carbohydrate moiety in elastin, hexoses showed definitely increasing tendency with age, but reverse was true in hexosamines.Higher total cholesterol and also ester cholesterol levels in elastin fraction from aorta were proved in sclerotic portion, comparing with adjacent normal portion.From these results it was highly probable that these changes in elastin during aging and atherosclerosis might offer the conditions, attributable to atherogenesis.