For 4 consecutive wk, 61 rabbits received weekly injections of lymphocytotoxic-positive human serum into the left carotid artery and of autologous serum into the right carotid artery as a control. Serum cholesterol and serum triglyceride levels were measured before the study, in the 2nd and 4th wk of the study and weekly thereafter. Repeated intimal injury caused raised, lipid-containing thrombo-atherosclerotic lesions and there was a consistent regression to lipid-free fibromusculoelastic plaques from the 1st wk after completion of the injection regimen to the 4th week. Apparently, regeneration of an intact covering cell layer resulted in the elimination of lipid deposits from raised lesions, resulting in lipid-free fibromusculoelastic plaques. In addition, fatty streaks occurred during regression. A statistically significant rise in serum cholesterol level during the phase of progression of lesions and a subsequent fall during regression were observed.