Purpose To identify matrix metalloproteinase (MMP) in human vitreous samples of diabetic vitreoretinopathy (DR) and other ocular diseases (non-DR) and to probe the related factors of MMP expression． Methods Thirty-one diabetic and 17 non-diabetic vitreous samples (nine macular hole and eight epiretinal membrane patients) were examined． Samples were concentrated and subjected to substrate zymography to conduct a quantitative analysis of MMP-2,9 activity． The technology of Western blotting against anti-human MMP-2,9 was performed to identify MMP in vitreous samples． Results Vitreous samples both from DR patients and from non-DR patients showed a single band at the position of 72 kDa, correspondin g to MMP-2． Quantitative analysis revealed that diabetic vitreous showed higher MMP-2 activity than non-DR, although the difference was not significant.45.2% of DR patients showed MMP-9, but no expression in non-DR．Among DR samples, the positive ratio of MMP-9 in partial posterior vitreous detachment (PVD)(66．7%) was significantly higher than that of complete PVD (15．4%)． Western blotting study confirmed the expression of MMP-2 and MMP-9． Conclusion There is no obvious difference of MMP-2 activity between DR and non-DR． MMP-9 may be involved in the pathogenesis of diabetic vitreor etinopathy and the deterioration of proliferative change． (Chin J Ocul Fundus Dis, 2001,17:195-197