We have analysed 11 trials which used quantitative angiography to assess the effects of lipid-lowering therapy on coronary atherosclerosis. Linear regression, weighted for the number of patients studied, showed that the change in per cent diameter stenosis was significantly correlated with per cent reduction in LDL-cholesterol (r = 0.74, p < 0.0005), but not with the LDL-cholesterol concentration during the trials. These findings have important implications for the secondary prevention of coronary heart disease.