Abstract： To the Editor:I congratulate Wang et al1 in reporting further evidence for the role of matrix metalloproteinase-9 (MMP9)as a biomarker in acute coronary syndrome (ACS).In this study,the Authors examined the levels of MMP9 and C-reactive protein (CRP) in patients with a clinical diagnosis of unstable angina pectoris who subsequently underwent coronary angiography to evaluate the presence of coronary artery disease.Two subgroups of patients were defined according to the presence or absence of significant angiographic coronary artery stenosis.The level of MMP9 was significantly higher in patients with angiographic evidence of significant plaque disease (plaque group) compared with those without significant coronary stenosis (non-plaque group).No significant differences in the levels of CRP were observed between the two groups.