Previous studies have attempted to demonstrate the reversibility of rabbit atherosclerosis after discontinuance of cholesterol feeding or by other measures. These attempts have been largely unsuccessful. In all the studies, atherosclerosis was induced by cholesterol feeding for several months. At the end of these prolonged periods, the animals had advanced aortic lesions. The present study sought to determine whether a shorter exposure to an elevated blood cholesterol might produce lesions that were reversible.Rabbits were fed cholesterol until their serum levels reached at least 1000 mg/100 ml; cholesterol feeding was then discontinued. Serum cholesterol values rapidly returned to normal levels. Some were killed at the time of discontinuance of the cholesterol diet and the others at periods up to 300 days thereafter. The aortas were removed and analyzed chemically for cholesterol content. The results demonstrate that cholesterol feeding of short duration produces a significant lesion whose cholesterol content may decrease markedly some weeks after the serum cholesterol has returned to normal levels.