The aortic connective tissue components, collagen, elastin, and glycosaminoglycans were isolated and quantitated from monkeys with experimentally-induced fatty streaks, from monkeys on a diet allowing regression of these lesions, and from controls. Although no variations were noted for total, soluble, and autoclavable collagen based on concentration, nonautoclavable collagen was significantly less (p less than 0.02) and elastin was reduced (p less than 0.001) in tissues with fatty streaks. There were no significant differences in total glycosaminoglycan content among the groups, but a large increase of hyaluronic acid (50 to 220 per cent) and a decrease of chondroitin sulfate C (40 to 66 per cent) occurred after regression. Dynamic alterations of arterial connective tissue shown to occur with induction as well as with regression of fatty streaks indicate the importance of connective tissue in maintaining integrity of vascular structures.