Several lines of evidence indicate that there may be an inflammatory component to the pathology of Alzheimer's disease (AD), the major form of degenerative dementia in the elderly. Activity of inflammatory cells, and the elaboration of toxic molecules by such cells may be a significant factor in disease progression. In peripheral inflammatory states, the increased activity of matrix metalloproteinase (MMP) enzymes are a major cause of tissue breakdown and secondary damage in diseases such as rheumatoid arthritis. The activity of such enzymes in the normal or diseased central nervous system is, however, not well characterized. We have therefore determined the levels of MMP 1 (collagenase) in the normal human brain and in AD. MMP1 levels were relatively low though were significantly elevated by approximately 50% in AD in all cortical areas examined. Given the activity towards collagen of MMP1, it is possible that enhanced MMP1 activity in AD, may contribute to the blood-brain barrier dysfunction seen in AD.