Chemical determinations of elastin, collagen, and creatine in the human thoracic aorta were made by Dr. Myers and Mr. Lang to determine the effect of the aging process on elastic and connective tissue, and smooth muscle. Eighty-three aortas were analyzed, the age range of the persons from whom they were removed at autopsy being 15 to 88 years. The changes observed in the mean values were in accord with the concept, r based on histologic observation, that elastin and muscle decrease and collagen increases with age.