PURPOSE. To characterize the expression of matrix metalloproteinases (MMPs) and tissue inhibitors of matrix metalloproteinases (TIMPs) in human cortical cataract and to determine whether there is a correlation with the localization of cortical cataract. To evaluate the expression and activity of MMPs and TIMPs after cytokine and UV- B exposure in a human lens epithelial cell line. METHODS. Twenty- eight human donor eyes with cortical cataract and 21 normal human donor eyes were photographed. Thirteen cortical cataract and six normal lenses were immunohistochemically analyzed for MMP- 1, - 2,- 3, and- 9 and TIMP- 1,- 2, and- 3. Twelve fresh cortical cataract and 12 normal lenses were divided into quadrants to quantify, by ELISA, the expression of MMP- 1,- 2,- 3, and- 9 and TIMP- 1. Three fresh cortical cataract and three control lenses were assessed for MMP- 1,- 2, and- 9 activity by SDS- PAGE zy- mography. Human lens epithelial cells (HLE- SRA- 01/04) were exposed to proinflammatory cytokines and UV- B radiation to determine the protein expression profiles of MMP- 1,- 2,- 3, and- 9 and TIMP- 1 and- 2. RESULTS. Immunohistochemical analysis revealed specific localization of MMP- 1 within lens epithelium and cortical lens fibers of cortical cataract. Normal lenses had equally low MMP- 1,- 2,- 3, and- 9 and TIMP- 1, - 2, and- 3 immunoreactivity, expression, and activity in all lens quadrants. IL- 1 and TNF- α upregulated the expression of MMP- 2,- 3, and- 9, and UV- B upregulated the expression of MMP- 1 in the SRA- 01/04 HLE cell line. CONCLUSIONS. This is the first study to localize the expression of MMP- 1 in cataracts with clinically observed opacification in vivo and to examine the expression induced by UV- B, in vitro. To characterize the expression of matrix metalloproteinases (MMPs) and tissue inhibitors of matrix metalloproteinases (TIMPs) in human cortical cataract and to determine whether there is a correlation with the localization of cortical cataract. To evaluate the expression and activity of MMPs and TIMPs after cytokine and UV-B exposure in a human lens epithelial cell line. METHODS. Twenty-eight human donor eyes with cortical cataract and 21 normal human donor eyes were photographed. Thirteen cortical cataract and six normal lenses were immunohistochemically analyzed for MMP- 1, - 2, - 3, and- 9 and TIMP-1, -2, and- 3. Twelve fresh cortical cataract and 12 normal lenses were divided into quadrants to quantify, by ELISA, the expression of MMP- 1, -2, 3, and- 9 and TIMP- 1. Three fresh cortical cataract and three control lenses were assessed for MMP-1, -2 and -9 activity by SDS-PAGE zy- mography. Human lens epithelial cells (HLE-SRA-01 / 04) were exposed to proinflammatory cy tokines and UV-B radiation to determine the protein expression profiles of MMP-1, -2, -3, and-9 and TIMP-1 and- 2. RESULTS. Immunohistochemical analysis revealed specific localization of MMP- 1 within lens epithelium and cortical lens lenses of cortical cataract. Normal lenses had equally low MMP-1, -2, -3, and-9 and TIMP-1, -2, and- 3 immunoreactivity, expression, and activity in all lens quadrants. TNF-α upregulated the expression of MMP-2, -3, and-9, and UV-B upregulated the expression of MMP-1 in the SRA-01/04 HLE cell line. CONCLUSIONS. This is the first study to localize the expression of MMP-1 in cataracts with clinically observed opacification in vivo and to examine the expression induced by UV-B, in vitro.