Recent advances suggested that proteases and their inhibitors could be implicated in the genesis and/or maturation of insoluble deposits associated with Alzheimer's disease (AD). This study was designed to measure the level of alpha-1-antichymotrypsin (ACT) and alpha-1-antitrypsin (AT) in cerebrospinal fluid (CSF) of patients with AD and nondemented humans at various ages. Our analysis failed to demonstrate a significant relationship between inhibitor content and disease. However, a positive correlation was observed between age and the ACT level for the normal control group. Such observation suggests a specific association of ACT with the mechanisms of brain aging.