This study was conducted to determine whether atherosclerotic lesions regressed in rabbits that were placed on a normal, low cholesterol diet. Rabbits (n = 16) were fed a 2% cholesterol diet for 90 days; nine rabbits were killed, and the remaining seven rabbits were fed a low cholesterol diet for 7 months.. Appropriate noncholesterol-fed controls were used with each group. After 90 days of cholesterol feeding, the rabbits' thoracic aortas showed severe lesions, accompanied by significantly elevated rates of collagen and noncollagen protein synthesis and significantly increased amounts of cholesterol and soluble collagen. Cholesterol-fed rabbits that were fed a normal diet for 7 months had normal serum cholesterol levels, but exhibited extensive aortic lesions with elevated cholesterol content. Biochemically, the rate of aortic collagen synthesis remained significantly elevated above control values; however, the collagen content was not different from controls. This lack of collagen accumulation in the presence of a prolonged increase in synthetic rate was surprising. One possible explanation is that in the diseased aorta there is a rapid turnover of collagen, resulting in a redistribution or remodeling of the connective tissue, rather than an increased accumulation.